# /etc/systemd/system/systemd-resolved.service.d/override.conf
  [Service]
  Environment=SYSTEMD_RESOLVED_SYNTHESIZE_HOSTNAME=0

[0]: https://github.com/systemd/systemd/issues/34897#issuecomment...

My field is networking, roughly from Ethernet physicals to TCP/UDP.

systemd has no f*cking clue what they're doing on networking. You need to not use systemd-resolved, and not use systemd-networkd or systemd-timesyncd either.

I really hope they are service manager people and know how to write a service manager, and I have no counterindications on that. But don't let them touch your networking, aside from service-managing on that.

(My recommendation for DNS - on servers - would be to install unbound locally and use that. It's not great for clients since it doesn't deal well with frequently changing network connectivity, or rather, it does, but only if you restart it on network attachment change, which implies flushing all cached data.)