This is looking like another good starting point:
https://drewdevault.com/2020/11/01/What-is-Gemini-anyway.html
I'm tempted to get his "suite of Gemini client software"... although I see I'd need to install the likes of gcc... overall a bit more rabbit hole than I'm up for at the moment.
But, if the protocol is really so allegedly simple, maybe I'll stare at this long enough:
https://gemini.circumlunar.space/docs/specification.html
and maybe feel motivated to put some Lua or Javascript into it.