Changing system font in macOS Catalina
Our only hope is that the gentleman who makes this tool figures out a way to make it work. I have been using this tool for years and has made my experience much nicer as I am not a fan of the San Francisco font. There was a few promising details in the issue tracker but as of yet no workaround.

https://github.com/jenskutilek/FiraSystemFontReplacement