p.s. As @jherazob has just pointed out, an alternative way to get media into a post is to embed it from another site. You can do this by just including the link in your post, it will automatically turn into an embedded player.
For example, to include a YouTube video just include the video's web link in your post. This also works with Bandcamp, PeerTube etc.
It can take a while for it to turn into an embedded player, so try reloading your post after a few minutes.