A bit ridiculous, but maybe the SmartTube app via Waydroid?
Not sure if that would operate well on a 4GB Pi.I suspect you'll either need to keep the Android System always running in the background and sacrifice some of your RAM or go through a slow cold-boot every time you want to watch YouTube.
That being said, privacy friendly? Eh? I guess more than the official App but I don't think they're explicitly doing anything for Privacy since their focus is making sure the app keeps working amidst YouTube's constant changes.
There's some browser extensions that let you run the YouTube Smart TV UI on your browser but not really private. You get uBlock at best.
The most private option would be a front-end like Invidious, but it currently doesn't have Keyboard Navigation, so possibly hard to navigate with a Remote Control, you'd need a mouse or similar device.There's a feature request for it but devs haven't gotten around it yet.
Maybe you could try to bodge it with a userscript? Idk.
For all that I'm scared this will enable terrifying new exploits, I'm equal parts happy all this proprietary crap is getting blown wide open faster than ever.
Hell yeah, fuck yo lock-in, fuck yo apps biatch 🖕