I sometimes enable the recommended videos in newpipe just to see what's out there, it's mostly shite, though. For me what worked was asking people. Sometimes my friends, but more often, hanging out in online communities/forums relevant to my interests gave me a bunch of good channel suggestions :)

I've been liking life with grayjay. No algorithms, no ads, no shorts. It's like "what if YouTube but not addicting?"

Same problem, interested in the solutions. Using a combo of Grayjay, like new pipe in which I have to subscribe to channels I already know, and YouTube.com in Firefox with sponsor block, specifically for the recommendation engine.

Not personalized. But what I personally use from time to time is the invidious popular feed, some invidious instances have the popular feed turned on, which shows popular videos streamed on that instance.

Instance list: https://docs.invidious.io/instances/

Example instance: https://vid.puffyan.us/feed/popular

Invidious has a related content option, it's in the settings where you should definitely already go to ensure the proxy option is turned on too.

Not exactly what you want, but below each video in freetube, there's an 'up next' playlist that afaik are still recommended. You can use it to find similar content.

You can DIY your own tool to scrape youtube.com for recommendations.