Sorry, I'm not using Safari playback for my app, so I haven't tried this.

Well you don't need it for iOS 15.1 at all, so I assume you are asking about it for macOS. I assume that is what they are going to do with macOS Monterey what they did with iOS 15. My guess is that SharePlay won't be enabled in macOS 12.0 and there won't be a profile anymore to enable it, but when the 12.1 beta comes out (likely in the next week or two), it will be enabled by default. In the meantime we can't test at all on macOS. This is a great system they have set up here.

And again, SharePlay is disabled in the macOS Monterey betas and the SharePlay profile to enable it expired on Oct 15, so I cannot test my app at all this weekend. This whole SharePlay Development Profile has been a complete disaster. I've gone weeks without being able to test and now with iOS 15.1 almost out, when I need to test the most, I am unable to because of arbitrary restrictions that make testing impossible. What a disappointment this whole process has been. Yes, I understand there is an Apple event on Monday morning and the RCs will likely come out that afternoon and SharePlay will likely work in them, but seriously this is such garbage and I feel like no one at Apple cares about any one actually testing their software. It's just roadblock after roadblock for no reason and it's broken literally half the time.