So Firefox (which I generally use) causes issues if I try http and puts in (forces) https regardless. I just logged on with edge and typed in http (which it still lets me do) and the videos show up fine. The move to https for all browsers has been brewing for a while now. It will get to the point where they will all insist on it (and this will be sooner rather than later). Upshot is all the embedded youtube in our posts will not display if your connection to the depot is https. The fix is probably rebuild the depot back end to the new code stream, again something we've been needing to do as we are on the old stream still. We are on the last update to the 2.0.x stream (2.0.19). SMF has moved on to the 2.1.x stream.
We may also have to go through all the embedded video html tags stored in the post database table(s) and convert fix them
. i.e. when we embed youtube videos in posts we just use the html youtube tag and just the videos ID, this get converted to the correct full URL/URI link by SMF and is probably stored as that link. So all the current videos embedded will have a http:// link which work if your browser connection to the depot is http. If, like when I use Firefox, the connection is forced to https, the links stop working.