What ISO did you use for your install ?
What changed before the error? An install? Update? Removal? How did you do that?
We can check if you are up to date:
sudo pacman -Syyu
The main issue seems to be
But that error usually happens when you dont have a desktop installed…
Also going to leave these just in case:
[HowTo] Resolve an unbootable Manjaro (black screen, login failed, cant boot, etc)
[HowTo] Provide System Information