Manjaro (KDE) not booting after BIOS splash screen - switching from old nvidia to 6900 xt

Hello,

If you can either chroot in or boot into runlevel 3
(see [HowTo] Resolve an unbootable Manjaro (black screen, login failed, cant boot, etc))
Then lets look at your drivers:

mhwd -l -li

If you have, for example video-nvidia then remove it:

sudo mhwd -r pci video-nvidia

Then maybe try to force reinstall the open drivers (this should be your only gfx profile):

sudo mhwd -f -i pci video-linux

Then reboot (systemctl reboot)