You can also link a direct video link, like ![](https://link.com/video.mp4)

Probably upload to YouTube or peertube or some video hosting site then post the link here.

Some PeerTube instances should allow federation over here. Just tag the appropriate Lenny community.

Depends on the instance. I can upload videos on my own instance but I guess most don’t allow that to save space.

Edit: Also see rule number 3 of this community.