Yeah, it’s impressive indeed.
Simmons has been developing macOS applications for a long time, e.g. when he worked for Omni Group. Here’s an interview from 2003 where he talks about an early version of NetNewsWire: https://daringfireball.net/2003/03/interview_brent_simmons
Ah dark knowledge through blood sacrifice. Was hoping they'd found an easier way :( Thanks for the pointer, been a bit since I read some OG John Gruber