For the last few weeks, I’ve been using yewtu.be (or another Invidious instance) when I want to watch a YouTube video. Piped and cobalt.tools seem broken for a while now… And I mostly use the FreeTube desktop app on my PC anyway.
I haven’t had any issues. For any clock/alarm app, make sure the app can run in the background and has the right permissions. If you encounter a bigger issue you can ask for advise on the Graphene OS forum.