PixiTracker format would be an interesting format, considering its limitations. It is easy to use. You can pass in some bitpacks using the .pixipack file format, which is basically a sample pack with 12 sounds. It has its own file format, which is .piximod. There is also PixiTracker 1bit, which is reminiscent of the old computers and their 1bit speakers.

Download link: https://www.warmplace.ru/soft/pixitracker/

The only thing that worries me is the fact that it is paid on Android and iOS, but I think it is fine because it is free for PC.

sunvox is also paid for android/iOS yet it has a format here..
should be fine

You wouldn't believe how many of my entries start here because of its xm export. It's like a mobile gateway to a myriad of formats