@yatil @help Micro.blog supports following websites with feeds. But it assumes one (sub)domain = one feed. So, following website like yatil.net works fine. But you can't follow any RSS feed. This one won't work because it breaks the assumption: www.youtube.com/feeds/videos.xml?channel_id=UC3KEoMzNz8eYnwBC34RaKCQ.
www.youtube.com offers more than one feed (many more).
fed.brid.gy is another domain that offers many feeds via redirects. So Micro.blog gets confused. How it decides what to include on the timeline when presented with a multi-feed domain is a bit of a mystery. Only @manton knows the answer. 😊