The dirmngr(8) man page says:

  The keyserver hkp://keys.gnupg.net uses round robin DNS to give
  a different keyserver each time you use it.

However, this is obsolete and no longer works: "gpg --recv-keys ..."
yields an error "gpg: keyserver receive failed: No name".

This is confirmed here:

https://stackoverflow.com/questions/66217436/gpg-keyserver-receive-failed-no-name

I've reported a bit more general bug at https://dev.gnupg.org/T5527
about keys.gnupg.net.

Control: tags -1 - upstream

According to the reply upstream, keys.gnupg.net is still documented,
but should work as its handling is now hardcoded (as of 2.2.29, thus
not yet in Debian). This may be OK for the upstream distributions,
but certainly not for Debian, as this would mean that dirmngr would
need to be updated each time some hardcoded server becomes obsolete
(I suppose that this is not acceptable for Debian/stable).

I'm removing the upstream tag, because this becomes a non-upstream
issue (upstream doesn't plan to update the documentation as
keys.gnupg.net still works with their solution, though the effect
may be surprising for users of different machines with different
GnuPG versions).