What players are supported? What if player doesn't support equalization?

Players such as Spotify, YouTube Music, Deezer (enable Equalizer in their settings), Yandex Music are supported out of box, player app restart may be required once.

Players that don't support equalization (such as YouTube video, TIDAL) still can be equalized via Advanced Player Tracking options in Equalizer settings, but that requires additional permissions.

See Settings / Equalizer / Advanced Player Tracking for step by step instructions.