Can't install Aptoide
Figured it all out!

Apparently Aptoide-dev was installed but somehow only for the guest user.

All I had to do was switching to the guest user, going to Settings -> Apps and remove the Aptoide-dev package.

Going back to my profile did some weird stuff (I can't switch between apps, it'll probably work after restart) but I managed to install Aptoide finally.

Thanks.