I had the same thing but no luck editing the project.uproject, (it didn’t have the “Plugins” line in the code.) Also tried DuyBaoTram suggestion, but my files aren’t laid out the same way. (Maybe cause I’m on a mac?)
Finally got it working by uninstalling the latest MagicBullet plugin using the Maxon installer, then re-installing an old version (It gives you that option once you click “install”) I went back to the version I had when I installed UE 5.3, then it worked, but only after restarting my computer.
Hope this helps someone!