Well, I've been beaten to the punch. This is a better first post than I would've managed to write. Personally, I think it's a shame that he had to have a thread, even though he deserved it, because of SourceHut. I so wanted to believe he could separate his Free Software activism from the rest of his politics and make it work, but he's made it clear he'll destroy it eventually. I look forward to finishing my dive through his forum posts and sharing what I've found here. A post here and a post there is so much easier to write than a new thread.
For now, I'll explain Gemini. To understand Gemini one must first understand Gopher. Here's the IETF RFC for Gopher:
https://datatracker.ietf.org/doc/html/rfc1436
To be brief, Gopher has seen more usage lately, and people have been abusing the protocol by adding new item types and other things in ways that go against Gopher's very basic design. A guy named Solderpunk decided to take these adjustments, and design a brand new, incompatible protocol around them. If that sounds stupid, that's because it is.
The main adjustment is the addition of mandatory TLS. The proponents of Gemini love to claim that implementing a client from scratch can be done over a weekend, ignoring how a TLS library must be used, due to the grotesque complexity thereof.
Despite all of the extra complexity, Gemini is incapable of any complex formatting, such as that available several decades ago on typewriters. If that sounds stupid, that's because it is.
Gemini also lacks very basic features such as download continuations, and I believe even download lengths.
The fact that nothing important has ever been written over Gemini and never will be is the icing on the cake.