Ok, I’m an idiot.
Basically, it was asking for the password multiple times for each and every process of the flatpak installation because of the mods I did on the system.
As a test, I typed the password as I was expecting for it to not be able to install as I get an error unless the super-user’s sudo is given.
Nevertheless, the package manager was running as a system process with its own sudo binary and it was enough to start the installation process.
Then, because of the way flatpaks are made, it has asked for permission to install other pieces of the software (I guess it was the locale package) and I didn’t give permission to the process the second time but the process just skipped the files I denied (not knowing as I wasn’t watching the terminal) and the app got partially installed.
Nevertheless, it has shown the “unable to install” notifications but that was only for the part of the package I didn’t allow.
Dunno if this is clear enough.
Anyway, you can delete the post if you want but feel free to show to the world how stupid I can be! XD