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https://www.steamgifts.com/discussion/v5uJ7/playnite-free-and-open-source-game-library-manager

It'll gain popularity ones everything moves away from only being on Steam.
I personally like it.

Hey, if it will let me search/sort by categories and tags, I'll use it just for more easily organizing all of my Steam games.

I much prefer LaunchBox. Its customization options are way more extensive, it has a couch mode called BigBox, community themes and its own database where you can pull all the artwork for your games. It has many years of development behind it too.
Downsides, it is not open source and the couch mode cost money. https://www.launchbox-app.com/

Playnite now supports Epic and itch :D

It seems like a great idea, and I'd love to have all my games in one place with one launcher. I've used it a few times in the past, but never stuck with it. It might require a combination of getting used to it and customizing it the way I want. Going to reinstall it now and give it another shot.