Litalino no, I don't believe the number of disabled extensions has any impact at all. On the frontend Flarum only runs code for extensions marked as enabled. Even in the admin panel Flarum reads the list of extensions from the Composer manifest file and doesn't read any file from the extension source until it's enabled (except for loading a custom icon if the extension provides one)
More disabled extensions only takes up more disk space and makes Composer slightly slower when installing and updating extensions because it will check that everything installed is compatible with each other, no matter if it's actually enabled in Flarum.
