Question regarding variable FPS for sprite sheet animations and the game itself

Hi! I’m an artist working on a 2D mobile platformer game, and recently created a jumping sprite sheet of 6 frames, meant to be run in 12 fps. The programmer in the team sent feedback that the sprite sheet was not smooth, and should be meant to run in 30 fps (mobile) or 60 fps (PC).

I’ve never heard of sprite sheet animations done in 60 fps, so I did quite a bit of research on the net, which states some games use variable frame rates, with sprite sheets running at a lower frame rate than the game itself.

1. Just wanted to check if this holds true for most games, or if I misunderstood something?

2. Is 12 fps not used to animate sprite sheets in 2D mobile platform games?

Any help is much appreciated, thank you so much!