I’ve tried Immich before and it’s fine for uploaded photos because it detects it’s the same photo even if you rename it. But as long as it doesn’t do that for photos from external libraries I can’t trust to put anything into its albums. And if I can’t use its albums to organize and everything is dumped into one big pile it’s a show stopper.
The only workaround I can think of would be to make multiple users and load different external libraries to different users, but it’s not a great solution. The mobile app doesn’t support multiple users anyway, I’d have to logout and login all the time.