This is good, and I wasn't aware GitHub had done that, too.

I'm still lamenting the state of Wordpress default themes.

Twenty Twenty One (which I'm using now) also uses the system font stack, but has made weird choices. Huge post titles (48px), titles are underlined, other things make for a suboptimal reading experience.

Twenty Twenty had this really weird font experiment with a variable font (Inter) that was unreadable on some devices (the font outline was… wiggly). Of course you needed a plugin to switch it off.

Twenty Sixteen (which I was using before) is really nice, but comes with a web font.

I'd love Twenty Sixteen with support for newer developments (like those block things), but without the need for plugins to switch off the font and a few other annoyances.