It really depends on what you find hard or easy about practice. Do you have any thoughts on that or examples of what you think would be easy for you?
Also do you have in mind certain types or genres of games like real time action/fighting games with bosses? There are also multiplayer games, shooters, platformers, turn based strategy games, speedruns, challenge runs, board games, all sorts of stuff.
There were some old discussions at FI or curi.us where people were practicing Mario Odyssey or Smash Bros. Melee.
I think fast retries is one of the things you want. I like that too.
I like Hollow Knight. One day Silksong will come out 
PS Did you ever try Toki Tori? I like it. But it’s a puzzle game, not something you really practice in the usual way. And some of the puzzles are pretty hard (but the gameplay is easy to control, you can rewind mistakes, and some early levels are easy).