Just installed KDE Neon 6.2 to evaluate. While the live cd did boot fine into the UI, after the actual installation and booting through GRUB (dual boot with Windows) the system gets stuck at a black screen.
It’s not even possible to switch to the alternative text consoles(?)
So I tried the second entry in the grub advanced boot options (sadly, the menu text is too long and cuts off the important last words that make the difference) and ended up in a “recovery” menu. So basically Grub seems fine.
Next reboot I tried the “edit grub config” and after some trial and error I found that if I remove the splash from the linux line in grub config the system does boot into KDE
I haven’t experienced it myself, but have seen a few random posts of folks with odd issues where their graphics card and the splash screen just don’t work well together.
One way to check that might be to temporarily add back splash in the same Linux command line that you removed it from, and then also temporarily add nomodeset (disabling graphics drivers from being loaded at the start of bootup) in that same line.
If the splash screen works with those parameters, then there’s likely some odd incompatibility among the combination of the Ubuntu/Neon splash screen, your particular graphics card, and the particular AMD drivers included in the Ubuntu 24.04 base.
It would also be worth double-checking that you have all available software and firmware updates installed from Discover when you are booted into Plasma.
If you want to go deeper into the system logs, you could also check what logs were created by the previous boot using the command sudo journalctl --boot=-1 and checking the end for any possibly helpful clues.