How to get Fedora 35 to use DNS name as hostname?

[Thomas Cameron]

It looks like the hostname is set in /etc/profile to uname -n, which 
means every instance I spin up thinks its hostname is "fedora." I don't 
want that. I want each hostname to set its hostname to whatever its DNS 
name is.

We used to set the hostname in /etc/hostname to localhost.localdomain, 
and that would be substituted to whatever the DNS hostname associated 
with the system's IP address was, but that doesn't seem to work any more.

What is the preferred way of having Fedora 35 server instances use the 
host's hostname from DNS? I notice that if I restart 
NetworkManager.service, then the reverse DNS hostname is set - hostname 
gives me host123.mydomain.com. I want to make it happen at boot. It's weird.

Thomas