On both versions of MacOS, that method was getting called. On Sonoma, the error parameter was sometimes a null pointer, and on Sequoia, in the cases I've seen, it's always a pointer to a valid NSError object. So the situation is a little better in Sequoia, but the system is still stopping the stream, and it's unclear why.

Nope. I ended up upgrading to Sequoia and things were more stable, but eventually the system would randomly cancel streams and would leave the menubar stuff until a reboot. On Sequoia, I DO get a valid NSError which says that the system stopped the stream, but I haven't investigated further

Nope. I ended up upgrading to Macos Sequoia and things were a bit more stable there, but eventually, I ended up with similar instability where the stream would stop randomly, and the menubar stuff would stay around until a reboot. The screen/window picker widget stopped working reliably when the OS was in that state. When running in a debugger, on Sequia, I at least DO get a valid NSError saying that the system stopped the stream, but didn't see any additional info about the cause.