In reply to Tom.

Agreed, this has been missing from the discussions I've seen. Worse, it seems there's currently no reliable data for macOS usage due to Apple blurring Catalina with Big Sur: https://bugs.webkit.org/show_bug.cgi?id=216593. Reading through the Trac ticket it feels like there's a number of hand-wavy dismissals of potential issues, though this Safari one seems the most problematic.

Anyone doing decent browser testing must be encountering this, so it's hard to understand how this hasn't been considered a blocker.