This app was mentioned in 7 comments, with an average of 1.43 upvotes
It's not easy to make an incredibly strong engine like Stockfish, play at an inferior level. The most common way to achieve this, is to force it to make extreme mistakes by selecting moves it knows are bad. It just feels very artificial and unnatural.
A good computer to play against for humans, is the Playmagnus app (iOS link and android link). Each level is more carefully tweaked so that it plays more natural.
Play Magnus - Chess. It's unpopular enough that you might not have heard of it. The game is just chess but you're playing an AI that's given a skill level depending on what age of Magnus you choose. So if you pick an age of 8 you'll be playing an AI close to the same skill level Magnus had when he was 8. It's fun for people who already play chess and people who want to get into it.
I honestly like the chess app play magnus. I can make it up to about age 12 and I get my ass handed to every time. There is an apple version as well but that's the one I had on hand.
It's called Play Magnus!
Links for Web, Play Store & iOS
Play Magnus app.
Play Store link - Play Magnus