while running the DVD (solus live environment), open the Gparted tool.
Your existing Ubu will show a 1MB boot partition, then a swap, then the system files.
If there is no space then after that, then Solus may offer to shrink the Ubu crap ("Install Solus Alongside of X") option.
If there IS a bunch of room for Solus then highlight the non-Ubu space in Gparted and format it to GPT.
Hopefully Solus will direct itself there.
OR
Solus should give you the opportunity to direct the install there (there=new gpt partition).

Since we don't know that...
...in fact there are still important things we don't know, chiefly because I suck going back and re-reading...

at what exact point in the GUI Install process does Solus fail? What step? What does it say? Does it just freeze? Or abort? Send a pic of what it looks like when you open Gparted in the live dvd. That will help. Pics of the wife not necessary😉
edit/punctuation

    blueicetwice OpenGL: renderer: GeForce GTX 560/PCIe/SSE2 v: 4.6.0 NVIDIA 390.157 direct render: Yes

    this will be deprecated (unsupported by nvidia) in solus and the homegrown Nouveau will work fine.
    I did not get the impression your Gigabyte product is "too new" for Solus--that's where common installs for 4.4 fail (new ISOs coming as you know)

    EDIT: XFCE may be a month of two away if I had to guess as an observer. try budgie.

    other thoughts: re-burn your Mate DVD for the hell of it. Pay attention to Solus's prep demands. I always find if I deviate then I've made a live medium useless and I try try again.

    Question remains: at what stage does install Fail?

      With 3 disks is this a multi Os boot setup?
      If it is might explain it (I am no expert at multi boot)
      Lunch time..lol

        brent

        Brent, my rig will not allow for GPT partition ! Both "disc" and "geeparted" show
        a successful installation, with Das Boot. Neverthebloodyless, when starting the boot
        it is not in the boot option. Odd, however, it does show up in the Grubhub Customizer. !

        I can not load any pixs, Brent. There were two abortions and the others stated "successful
        installation." Could this be an Ubuntu or Mint ploy or plot ?

            Axios

            AX, fix this issue and lunch is on me.

            I have tree HDD, with a single OS and each. I try not to comingle.

            The only multi boot dat I understand, was in basic training.

              blueicetwice ......in my limited understanding, the bios just guarantees a Grub install (I think) and Solus would meke the Grub partition itse;f..still don't see the correlation.

              It is utterly mindbogglind to me that Solus tells you installation was a success on boot then aborts on launch...

              To me this means one of two things:
              1) incompatible Graphics card (longshot)

              2)Or more likely Axios is right: the other jealous distros are interfering. My advice is UNPLUG the other two then boot solus again. I am predicting success. Something is goofy in the boot then if what you say (Solus says install was successful) is correct.

              Hang in there. this distro is well worth it and I've tried most.

                    D/Led GOGONOME and was told the installation was successful. Fabulous how the
                    screen slowly fads into darkness ! Brilliant engineering.

                    Upon restart, the issue again, Solus was not in the boot up order, even tho it was listed
                    in the Grubhub Customizer.

                    It has been a joy to communication with y'all, butt this is truly a waste of time, despite
                    being on home detention. 🇧 🇪 🇩 🇫 🇪 🇪 🇧 🇦 🇩 : <---------- my imoji are blockheads : - ))

                    blueicetwice reinstall with others unplugged was probably the better suggestion, but all good.
                    "D/Led GOGONOME and was told the installation was successful." I don't know what means. The installer usually says at the end something like 'solus installed successfully'; or similar so if that's where you saw it...then grandiose🙂

                      Brent, what dat means the installation was successful, according to
                      ISO d/l disc.

                      I did another install and Solus populated the boot up order. Den,
                      which I click the Solus boot line I got this: "ERROR: file /Das Boot/Solus Project.
                      current.6.3.8-240 not found"
                      ERROR: you need to load Lt. Kernel first.

                      Another dead end ! : - ( Next try, I will UNPLUG the two other HDD and the ninth
                      reinstall. In the meanwhile, time for dinner. The wifi is serving stir fried hard drive,
                      with stuffed Chinese Dram.

                      I did to fail to mention, I am installing on an HDD with Manjaro on it, but dat
                      should not make a difference.

                        blueicetwice did to fail to mention, I am installing on an HDD with Manjaro on it, but dat
                        should not make a difference.

                        'Sometimes' it makes a difference is my cryptic answer to that. you never know til you know. e.g. a partner OS installed with Grub will unceremoniously mug, then disappear, Solus' UEFI bootloader (if installed that way) about 8 times out of 10 if I had to guess and 10/10 for me personally (that's why separate drives per OS for me). Maybe it was Manjaro in the cellar with a candlestick (to bludgeon a Clue metaphor) the whole time?

                            brent

                            "Maybe it was Manjaro in the cellar with a candlestick (to bludgeon a Clue metaphor) the whole time?" LOL, LOL

                            (that's why separate drives per OS for me) ditoes for me, as well, Brent.

                            If Solus has a UEFI bootloader, den dat may explain the problems, since my mama board is
                            not compatible.

                            Hear, is what happen last night. I disconnected the other two HDD, as per your instruction
                            and holey heck, the installation was successful, even after a fresh bootie. Watching the boot
                            lines, I noticed that the boot for Microgates 7 and Minty Mint were absence. 🇧 🇦 🇩 To
                            quote Ms Greta Thunberg, "this is all wrong."

                            When I had only the Mint HDD plug in, the old bootloader lines appear !! Unfortunately, Solus
                            bootloader was not present. : - (( I now suspect it is not Solus fault, but rather my dated Mama
                            board. It is likely, I will have issue with other Linux discos, as well.

                            Brent, tanks for your support and the others, whom had commented. I have boarded an engine
                            power vessel, thus allowing Solus to sail to its next destination, less my baggage.

                            PS: This was not an issue, when I installed Solus some ten years ago.

                                blueicetwice Solus defauklts to UEFI install but can be made (in the installation GUI I believe) to installal GRUB boot instead. I have never tried this.
                                Either way, I agree, you tried.

                                    brent Its amazing the countless threads I have seen on here about Os,s not playing
                                    nice with each other.

                                        Axios yep it's happened to me with linux and windows. Solus get's bullied a lot in my experience, probably because efi bootloaders is alien to most things grub and also to windows who has a bootloader...although I saw a single instances here recently where someone claims Solus wrecked all their other existing boots but I've never seen that. Strange times!

                                          9 days later

                                          UPDATE for my mates.

                                          I tried two more installations and botf failed. Since Mint took a powder on me,
                                          I decided a last attempt, with Solus 4.5 XFCE. Now the installation was NOT
                                          a dual bootie, but a single installation on the entire HDD.
                                          HOLEY VACA [COW] <---- Latin, it not only did it install, but bootied up as well !!!!!!!!!!!!!!!! :<))

                                          Brent, was right about the problems with dual OSs, on a single drive. Same issue when da wifey
                                          is driving.

                                          The grubhub found itself on another HDD, so it required the change in HDD start up order. I bet if
                                          I try to reinstall MInty 20 next to Solus, it will fail too.

                                          The installer is the BEST I have ever used; quick, easy and with clear instructions. Mint installer, [21.3]
                                          is rather AARPish and much slower. And it was not the UEFI nor the advanced kernel, which
                                          I speculated as to the issue, in this twelve-year-old rig.

                                          I wonder what I should do with MInt ??? There is an orphanage just three miles from me.

                                          ![



                                          I used to bee Solus, until I got married.

                                          I should add, dat Solus was installed as an EFI. None of my
                                          other partitions have this classification. No DEI installations,
                                          tank goodness.

                                          Five stars to Brent on Google Map, for his suggestion, which lead
                                          to this success !!