https://forum.endeavouros.com/t/bash-append-path-command-not-found/8049
This happened to me after last system update. After inspecting /var/log/pacman.log to see what changed, I found this line:
warning: /etc/profile installed as /etc/profile.pacnew
Updated packages were filesystem, perl, srt and sudo.
/etc/profile is used to set system wide environmental variables on users shells.
/etc/profile contained appendpath function declaration, /etc/profile.pacnew contained append_path
If that is also your case, try renaming
/etc/profile => /etc/profile.old
/etc/profile.pacnew => /etc/profile
Hope it helps.