If the rfc822 style debian.sources format is being pushed for Trixie, then there should be a debian.sources(5) man page which documents it. Even if debian.sources(5) simply redirects to sources.list(5) showing both formats, that should be enough.
No that's wrong. debian.sources is the sources for the Debian Operating System; not the name of the format. My preferred manual page would be apt.sources(5). Otherwise we end up with $vendor.sources manual page symlinks on each os vendor, and it particularly gets weird with downstreams that do not rebuild apt.