I know how to read music and started taking classical lessons as an adult. Some time last year a friend recommended me to check out Melodics. It has 3 instruments: keys, pads (finger drumming), drums. I've played pads for few mont;hs, that was good, I've felt it improved my timing and rhythm skills quite a bit. Then I switched to keys. I didn't really like that; it felt like I'm mindlessly repeating whatever is on the screen instead of internalising music. OTOH, when playing pads it felt that something stays in my head after playing. So I guess this may be useful to some people.
For me it'd be more interesting to have some sort of memory trainer - I play something on screen few times, then I replay from memory and app shows me a diff maybe? Or when I'm learning a piece, it would give me a challenge "play bars 21-25 both hands" or "play bars 19-23 left hand only".
[1] https://melodics.com/, I'm not affiliated in any way