I watch YouTube through newpipe, and recently tried pipepipe too. They work great, but lately I have been blocked on several occasions with a message that either says "content unavailable" or "your IP has been blocked by YouTube". I usually use a VPN which has helped but tried it today and still got this message :/
Finally changing the location on the VPN seemed to work. But seriously wtf is going on?
You could check out PixivEF, as well as Pix-EZviewer. They are both open source frontends for Pixiv. Not sure if it fits your needs but they are decent options