Depends on the instance, it might be down or having work done on it, and also I think there might be some ongoing war with youtube api to keep everything working but im not sure. I just signed up on the kavin rocks one, every couple of days it will be down for a bit but it comes back up.
Try piped. Your feed is only what you subscribe to and theres a toggle to hide shorts
No I dont think so. Theres a trending page on a feed page