This used to be a great open source addon for removing clutter from Youtube (not just recommendations).

However, the developer has recently disabled almost every feature in the addon (except the ability to remove recommendations and disable shorts), requiring you to pay to restore the majority of the functionality. In addition to that, the addon now not only collects data on you, but the author has recently been committing a bunch of LLM generated code to the repository. I would stay away!

If you just care about removing recommendations, this might still be an option for you (although I would recommend uninstalling it). But for decluttering the Youtube UI, you can do what I did and instead use YouTube Redux, another addon, which is still open source and free as in beer. In fact I actually like that one a lot better, because it does an even more complete job of fixing the YouTube UI.

YouTube Redux doesn't actually remove recommendations or disable autoplay, so you'll still have to find other ways to accomplish that if you want to. I actually found the recommendations that YouTube Redux shows to be so unobtrusive that I didn't even look for ways to disable them, and autoplay can be disabled by other means (for example, if you don't want to sign into Youtube, there's a reddit post you can find of a single line you can add to your uBlock Origin filters that blocks the autoplay Javascript, and there are other addons that accomplish the same).