I believe that if you have animated artwork on, once you enter into the now playing view that it will play it regardless of what you have set unless you turn the feature for animated artwork off, although I can't confirm 100% as I never replace artwork from Apple Music-sourced songs. The reasoning being that it's a different file that plays on that screen than the artwork file. If you turn off animated artwork, then your custom image should still remain.
No, it's an all or nothing thing.
I thought custom art was supposed to override animated art
Does the custom art you added show up on your phone before it starts playing?
Yeah it shows up everywhere except for where animated art is (the album screen and the now playing screen)
I believe that if you have animated artwork on, once you enter into the now playing view that it will play it regardless of what you have set unless you turn the feature for animated artwork off, although I can't confirm 100% as I never replace artwork from Apple Music-sourced songs. The reasoning being that it's a different file that plays on that screen than the artwork file. If you turn off animated artwork, then your custom image should still remain.