BuzzPCSOS Could not replicate the fault on the BIOS screen.
That suggests that the issue is not a hardware issue (onboard UHD 620 failure, connector cable).
However, I think that you might want to consider running Dell ePSA pre-boot diagnostics as the next step. You can access the diagnostics by repeat-clicking F12 and then selecting "Diagnostics" on the Boot Menu. The diagnostics take time to run, but a clean diagnostics report will help rule out a hardware problem.
BuzzPCSOS Should probably try again with some other OSs now that I know how to replicate it.
If the diagnostics report no issues, then trying with other OS's makes sense as the next step.
If I may make a suggestion, I would, were I in your shoes, install two operating systems in this order:
(1) First, I would install Windows 10 (the OS that came with the computer) because installing Win10 will allow you to bring the BIOS/firmware up to date easily from the Dell Latitude 7280 Support "Drivers & Downloads" page. If there is any kind of a firmware issue involved, bringing your firmware up to date might solve the problem. I've noticed on my Dell Optiplex and Latitude computers that Intel chipset and firmware (including graphics firmware) have updated several times in the last year or two, so outdated firmware could be an issue. I would install Win10 using the Media Creation Tool (MediaCreationTool22H2-W10.exe) available on Microsoft's Download Windows 10 page. That way you'll get a clean, current version of Win10.
(2) Second, I would install the official Ubuntu flavor corresponding to the Solus DE you are having issues with (Ubuntu for Solus Gnome, Ubuntu Budgie for Solus Budgie, Kubuntu for Solus Plasma, and Ubuntu MATE for Solus MATE). I suggest Ubuntu and official flavors because Ubuntu is, like the UHD 620, ubiquitous, has an enormous array of support pages/forums, and installing the corresponding flavor will put you into the same DE environment as you using on Solus.
If you get the problem on Win10 after all the firmware has been updated, then we are looking at a hardware problem of some sort. If you don't get the problem with Win10 but do get the problem with UbuntuX, then we are looking at something to do with the Linux kernel and/or a driver. If you don't get the problem on either Windows 10 or UbuntuX, then the issue is probably related to Solus. That's the troubleshooting path I'm suggesting.
The Latitude 7280 is a great laptop. I bought one in early 2017 and used it daily until a grandson caged it off me a year ago (puppy eyes still work at 14). It is well worth the effort to chase this issue down and solve it, if possible.
I did a bit of research about the issue yesterday, and UHD 620 screen flicker does happen sometimes with Linux. In the cases I read about, the issue seems to be driver corruption of one sort or another. That doesn't seem real likely in this case, because you get the problem with both the Live (5.15) and the current (6.1) kernels. That's one of the reasons I suggest an Ubuntu flavor as an exploration distro. Ubuntu has about a 40% Linux market share, so if there is an issue, the Ubuntu forums will have dealt with it.
