On the fbdev parameter, I’ve read contradictory information. See for example here which says to set fbdev to 1 for a particular use case for kernel >= 6.11. I’m on 6.11, but I don’t have two DRM drivers and I came across a recent comment on ArchWiki to set fbdev to 0 for kernel >= 6.11.
I know you are not on 6.11 and none of this may apply. You may want to try the 6.11 kernel out though if that is an option. You’ve probably already gone through the wiki, but if not, see NVIDIA ArchWiki for help configuring.
I see the version shown for your nvidia driver is 560.35.03. Did you choose not to downgrade to 550.120?
I was remembering
Nvidia drivers got downgraded to 550.100 , therefore update with
sudo pacman -Syuu. If you want to stay on the 555 driver series you may either switch to unstable or install nvidia-dkms via:sudo pacman -U https://mirror.easyname.at/manjaro/pool/overlay/nvidia-dkms-555.58.02-1-x86_64.pkg.tar.zst. More info about Nvidia drivers here:555 release feedback & discussion - Linux - NVIDIA Developer Forums
550.78 release feedback & discussion thread - Linux - NVIDIA Developer Forums notification here