It appears that the recent update to macOS 10.15.7 Catalina (Security Update 2021-007, released on 25 October 2021) causes WebGL to fail on certain Macintosh models. This affects all websites that use WebGL. as well as applications that use WebKit.
See for example:
It appears that Mid-2012 Macbook Pros running Catalina have …https://www.reddit.com1. ‚Ä∫ apple ‚Ä∫ comments ‚Ä∫ it_appear…
2021-007 Security Update Catalina causes - Apple Support …https://discussions.apple.com1. ‚Ä∫ … ‚Ä∫ MacBook Pro
Since iScreensaver uses WebKit and WebGL internally, this also affects iScreensaver.
We are following the issues and will report back here if there is an update to fix the problem.