https://gamefaqs.gamespot.com/boards/189706-nintendo-switch/79890338

I used Backlogery, but Backloggd seems to be more popular nowadays. That forum discussion mentions a few others, too.

If you play retro games, then you could also look into RetroAchievements, which will track more than when you simply beat a game. Unfortunately, it doesn’t work for all games though.

For more modern games, you could also use Achievements to track what you beat.

As for keeping track of what games you WANT to play… it’s called buying them! Don’t buy games you don’t want to play, haha

Seriously though, you could go through your Steam library and add games you want to play to a playlist, or sell physical games you wanted to support but don’t want to play.

But for multi-platform stuff, check out the linked forum post