MacWhisper Pro supports this, if your need for this is time-sensitive. https://macwhisper.helpscoutdocs.com/article/32-automatic-sp...

You are looking for speaker diarization. No one is doing this well currently on device (in macOS land at least).

No, not yet! That will definitely be included in the next update next month. Thank you for reminding me of peoples unique need for this use case