I’ve the same problem, however my case could be different from @aldobelus.
In our environment, discourse is part of a bigger portal, which loads each component in an iframe.
- Full-screen button exists, if I open the site directly in a new tab.
- Full-screen button is missing, if I open the site in iframe. In embedded videos, it’s so to say iframe in iframe.
The video itself is available and playable in both cases.
Has anyone an idea what could be the problem and how to troubleshoot?