Tangental: Came across an app aspiring to be 'duolingo for math', could the same be possible for music. I played guitar for ~10 years yet if I hear two tones, I struggle to tell which is higher and which is lower! (unbelievable that it would be so hard, when others have relative/perfect pitch!). So you could do duolingo for tones, or duolingo for modes etc.

Very Tangental: I had another idea for a 'music' game. Years ago, I used to mumble. People couldn't always understand me. So I randomly made a collection of phrases I struggled to say crispy to practice them 10 times each per morning. It improved my articulation a lot. I sometimes do the same (as a form of vocal exercise) but I made it way more fun by putting on one of my favourite rap tunes and cranking up the playback rate. For example chance the rapper's 'no problems' or 'angel' at 1.5 speed is a great vocal exercise. Perhaps this could be gamified. (I guess technically, it already is, as it's already a fun way of doing a boring task).