I'm having the same issue on Freetube, it pops up and says it can't play the video because Youtube requires being signed in. Sometimes if I retry a couple of time it'll play, but usually keeps getting the same error. Freetube is great though, maybe they'll come up with a solution soon.
I had a private invidious instance, with the bad idea to be attached with my paid domain, and even it was private , google crawl bots listed it into the Google Safe Browsing blacklist. In consequence, my domain admin (NJALLA) banned me: i had 1 year paid, they didn't refund, and imagine the disaster in all my self hosted apps.
Unfortunately, neither fixes this. Grayjay seems to work, but its inconsistent in my experience, often repeatedly returning to the beginning of the video part-way through.
Grayjay is useless on Linux. Every video suddenly stops halfway and you need to reload. Same for every video. Talking about music videos, 5-6 min long.