Exotic harddisk (new) ...

the Seagate HDD comes pre-partioned? That doesn't seen normal. Smells like a refurb,

Either way you will know if your GPT formatting works when you install an OS on it successfully.
If this was me I would nuke the whole HDD, partitions, data and all, and re-do it pure GPT. It's hard to tell if there's some relationship between the two partitions.
A weird problem to be sure.

what makes you think the solus iso is unclean? because it won't install? or because gparted is wiggy?

the only times gparted thows errors for me is when there is permission problems...
the only time I can't get Live Solus to install on HDD is when the disk is not formatted properly to be installed on.
unless the LUKS part is doing you no favors?

256 TB drives don't exist, and they especially do not exist for 25 Euros. Scammers will sell hard drives and flash drives rigged to report they hold more than they actually do, when in reality they're much smaller cheap drives.

DirtyAngel Well you bought a hard coded USB flash drive, so it will not work for OS install.
Device 015 USB hub
Device 016 & 017 are the partitions.

An OS first reads Device 015 = USB hub not a bootable location thus it will not read/mount/install

The backup GPT table is corrupt, but the primary appears OK, so that will be used.

after reading the two posters above me and re-reading the whole log (it was longer than I thought) there is so much strangeness going on from residues of old data I wonder if you should just bite the bullet and let DD zero this disk out a few hours then start over? maybe fsck could some of the lifting?
I can't escape the conclusion it's no good to do anything on this disk without a serious scrub. 2 cents

brent I can't escape the conclusion it's no good to do anything on this disk without a serious scrub.

I agree. I've been there before, and at some point, the time and effort to do a reinstallation is far less than dealing with continuing problems. Fortunately, Solus is very fast and easy to install and update.

DirtyAngel when I created successfully a partition then there pops up a new "undefined" file-system with size of 1 MB ... - well, then there is spyware or what as firmware ... ?!

spooky and unacceptable. never seen gparted do this. although that's about the size of a grub boot partition...
I am as reasonably paranoid as the next PC user and firmware malware is the next big attack vector (from my reading) so ya never know.

DirtyAngel but I don't know if this 256 TB size would then melt ... ?!?!?! How long would this last ?!

if it is truly is 256TB (did you verify?) then leave the computer on and check progess daily. I would guess 20 hours but I have nothing to base that on.

WetGeek I agree. I've been there before, and at some point, the time and effort to do a reinstallation is far less than dealing with continuing problems. Fortunately, Solus is very fast and easy to install and update.

too much monkey business on this SSD, yes

DirtyAngel It seems that GParted is not working correct ?

That seems quite unlikely to me, but you could check it by installing KDE Partition Manager. It's similar enough that you shouldn't have trouble using it. If you get a similar result with it, you'll have a better idea what's wrong.

DirtyAngel The only thing that's not working correctly is your fake drive. They of course had to do some trickery to make it report as a 256 TB drive, so that's most likely what trips gparted up.