Hi,
Welcome to Microsoft Community.
I would like to ask if you are currently using the latest version of Edge?
This problem is likely to be a problem with a certain version of Edge. I recommend that you submit this problem to the developer through the built-in feedback function of Edge.
In addition, I need to confirm with you whether all html5 videos cannot be played or is it an individual case?
Thank you for your patience and understanding!
Best regards
Manson | Microsoft Community Support Specialist