Pop-up appears and disappears too fast to read on startup.

I have a window pop up every time I boot my Mac. It disappears before I can read it, but the screen capture in the thread at https://discussions.apple.com/thread/254311463 looks similar. It's asking for permission for something like "mediasharing" to accept incoming connections. (I can't say for sure, because the box disappears too quickly to read it, let alone click to allow or deny. So it kind of smells like some kind of malware.) This started while I was running Ventura, and persists in Sonoma.