Dude, I’m reading through the package files now.
As an AUR package it’s not part of Manjaro and so doesn’t necessarily comply with proper packaging methods. You also can’t expect someone to answer the question in a ten-minute window.
It looks like the AUR package simply installs the launcher to
/opt/ankama/dofus, then when you launch the game it downloads the game files. When you uninstall the package,
pacman only removes the files installed by the package, not those downloaded afterwards.
Hence, the package leaves files present on the system after removal. This is a bad package. You should be able to remove all files after uninstalling the package by e.g.
sudo rm -fr /opt/ankama/dofus.
There may be other traces left elsewhere I haven’t spotted, but if you’re having an issue here you should post a comment on the AUR page so the package maintainer can fix it for everyone.