Safari 14.0 WebGL disabled?
In some cases WebGL is disabled in the Safari preferences.
AFAIK there is no UI to edit the setting. So you may need to edit the Safari property list file. It is located at
~/Library/Containers/com.apple.Safari/Data/Library/Preferences/com.apple.Safari.plist 

This is described in the following post:
https://discussions.apple.com/thread/251723774?answerId=253458486022#253458486022
The .plist can be edited with the “defaults write” command in Terminal, but this will work correctly only if Terminal has full disk access, as described in this article:
https://lapcatsoftware.com/articles/containers.html