As of about 15 minutes ago, SDL3 reached 100% documentation coverage. Every single public symbol in SDL's headers is now documented!
The massive list is here:
https://wiki.libsdl.org/SDL3/CategoryAPI
The much more pleasant way to browse this is here, though:
https://wiki.libsdl.org/SDL3/APIByCategory
(You can also download the entire wiki as static HTML pages for offline viewing, or even peruse them as Unix manpages. We're taking documentation very seriously in SDL3!)