26 face-to-face meeting in 5 years is an extremely low number; I'm glad to see that the developers of the Internet embrace remote work :)
For some newer work like QUIC, GitHub is used to maintain a more to-the-minute shared view of the documents, and then again as mentioned in the text you quoted, GitHub Issues and PRs are used to manage the document, particularly by the most active participants.
https://github.com/quicwg/base-drafts - of course raising issues or PRs for them now won't do anything useful for you, because these RFCs were published. But you can see there were thousands of commits, one of the last being Martin Thompson's minor typographical tweaks summarised as "DOES IT NEVER END?!?".