Oh, I forgot that https://arewebrowseryet.com/ exists for this too!

https://doc.servo.org/apis.html is auto-generated from WebUDL interfaces that exist in Servo. It's not great but better than nothing.

Closest is perhaps the web platform tests

https://servo.org/wpt/

There's a lot of work between the WPT team and web-features/web-features-mapping that should allow this to work automatically based on WPT results.

Their bloghas monthly posts on changes https://servo.org/blog/