Louis Rossmann unveils Grayjay - a video client similar to Revanced and NewPipe, but shows your subscriptions from various video sites in a single feed.
Site: https://grayjay.app/
Source: https://gitlab.futo.org/videostreaming/grayjay
The app is OSS but not Free, which I’m personally completely OK with.
Watch elsewhere: Invidious / piped link in comments
so, they have already blocked third party apps, notably when Microsoft and when Amazon made apps, both got blocked. So no not really, they can block whoever they want.