probably you installed something manually at some point, otherwise pacman does nothing wrong. Rarely you have to touch something manually because a mayor upgrade, but I think it has been like 4-6 times in 20 years for me.
If you want to install something manually in arch it is better to create a package first (if it is not already in aur). That way pacman can check for corruptions before installing anything
Pacman works when updating all packages simultaneously. However when updating only a requested package it can break by failing to pull in other packages which need to be updated simultaneously. For instance, pacman can break pacman and sudo by updating OpenSSL to a newer version than the currently installed version of pacman and sudo expect.
If you want to install something manually in arch it is better to create a package first (if it is not already in aur). That way pacman can check for corruptions before installing anything