The keys.gnupg.net keyserver is obsolete and yields an error "gpg: keyserver receive failed: No name" (tested under Debian/unstable with 2.2.27). This is confirmed here: https://stackoverflow.com/questions/66217436/gpg-keyserver-receive-failed-no-name
With grep -r keys.gnupg.net, I can see that GnuPG 2.2.29 (i.e. the latest version) still uses it and documents it. This should be updated.
GnuPG 2.2.29 does not use keys.gnupg.net anymore. What it does is mapping keys.gnupg.net that is read from an (old) keyserver setting in the configuration files to a (hopefully) working keyserver. The documentation of gpg and dirmngr does indeed still mention keys.gnupg.net. The main problem with updating the documentation is that there isn't a good replacement for keys.gnupg.net and since keys.gnupg.net still works (via the aforementioned internal mapping) it is probably the best option for now.
OK, thanks for the explanation. But I think that the documentation should be slightly changed to say that the mapping is hardcoded. Otherwise, this may surprise users of different machines with different GnuPG versions (or in discussions between different users), who would see different behaviors when the mapping changes.