Are both AUR packages. If you want to keep them, then we have to see their AUR page and move this topic to the right category.
If you want to use Manjaro provide gtk3 packages then: sudo pacman -Syu gtk3 lib32-gtk3
should fix it. Tou will have to confirm the replacement of the Aur packages when asked.
Released [/18.0.3/mGAMe-18.0.3-x86_64.iso]
gamer version, do not download it from the official page since I did not find it there,
Is the iso the problem?
The age of the iso certainly is an issue. You will get problems updating and theoretically have to read all announcements since iso release to apply all needed manual interventions.
Always use the newest official one.