Steam

If you don’t mind not retaining the original unlock date, there is a way you can reset all your achievements for a game.

You can do this via Steam Achievement Manager or via terminal.

That seems like a very niche thing, I'm happy with my 100% achievements and don't want that status gone. What you could do instead is create a new steam account and steam family share your games to that new account to play again with no achievements.

Not interested in that myself as I rarely replay games even more so to 100%

I enjoy collecting achievements, but I almost never get 100% of them - a lot of the games I play have achievements for finishing the game on several difficulty levels, and I'm definitely not 'autistic enough' for that. TBH I'm usually content with 50% achievements.

I can see the appeal for games where collecting achievements isn't extremely time-intensive, though.