Take a look into GrayJay. Open source app. Think it is made by the developers behind FUTO.
You can use several streaming services like YT and rumble in the same app, and make favorites stored localy on your device. You can even duplicate/import all your favorites from an existing YT account.
I think this is exactly what youre looking for.

The DuckDuckGo browser is all you need to watch youtube without ads.

Lauching a video hosting platform would be incredibly resource intensive. Proton should remain a privacy company first and foremost.

who would make the content that proton would offer? how would proton moderate the platform or catalog? how general or specific is the scope of the streaming service? how much would users pay for it? what would proton do differently than others? why would a streaming service fit with proton's existing products?

I think Proton has already tried to launch something like this in the past, but entering this competitive market requires a lot of investment and time. There’s no guarantee that a project like this will take off quickly; after all, let’s not forget that YouTube isn’t just another cute interface on the web—it’s a space where ordinary users integrate this video player into their daily routines, making it an extension of their thoughts. Proton should take this topic more seriously.

I had thought of that too, I was actually going to suggest it earlier, but I'll support your idea, I like it.