That is very, very new, and afaik it uses the poorly performing reference Implimentation.
HEIF works in Safari, and I believe Android will have it soon if it doesn't already. As for AV1, browsers can add it anytime they want…
Looking at CanIUse [1][2], it seems like the HEIF support is in macOS itself, and not the Safari browser. I wouldn't be surprised if the Windows version of Safari didn't support it.