I help with podcasts at Substack. Substack is a podcast-hosting platform like the others you describe (although in my biased opinion we have a number of other great features that set us apart). Most of the podcasts on Substack are hosted and distributed by Substack. A few Substack podcasts do point back at other platforms, but this isn't the norm.

Writers can embed youtube videos in their posts. When they do, those are hosted on youtube.

However, Substack also has our own hosted videos (see https://on.substack.com/p/video-on-substack).