What can I play without a big learning curve or grind?

For a simple loop with visible progress, you could try PowerWash Simulator. The jobs give you clear stopping points, and you don't need to plan a build or learn a pile of systems. If you want something more action-focused, Vampire Survivors has short runs and unlocks, though the screen can get busy.

You might get more out of returning to a game you already know than starting another big progression game. Since you enjoyed Witcher 3, try an easier difficulty and do one quest at a time, without worrying about perfect gear or guides. If you'd rather go back to a building game, consider setting yourself up with the storage and tools you want from the start, instead of making yourself repeat the early grind.