On the opt-in analytics:
They are anonymous and opt-in preference popularity analytics. You can preview what will be sent in settings. They are going to be used to determine what settings are popular and what should be the defaults.
You can find more info on the PR https://github.com/GeopJr/Tuba/pull/1166
The server's source code is located at https://github.com/GeopJr/Tuba/tree/main/server and is quite small and readable (#CrystalLang).
(unrelated attachments)