I try downgrading xorg-server, but strangely I do not have the required packages available in the cache and some are missing. @cantoraz Could you post yours for downloading?
Currently I try to fix Sudden crash&reboot with 5.10; with 5.4 not crash, but no graphic - #3 by kangaroo and maybe downgrading xorg and the relating xf86 packages is a solution…
I know there is a repository for old Arch packages butAFAIK they can differ to the packages from Manjaro so it would be safer to use yours.