By default TemplateVMs are not network enabled. They are able to update
because they use the Qubes Update Proxy. You can (and should) read about
this at
https://www.qubes-os.org/doc/software-update-vm/#updates-proxy
You hadn't said previously that you were using a minimal template.
Have a look at
https://www.qubes-os.org/doc/templates/fedora-minimal/
What you need to do is:
1. qvm-run -u root <template> xterm
2. (in template): dnf install qubes-core-agent-networking
3. Shutdown template
4. qvm-prefs <template> netvm sys-firewall
5. qvm-run -u root <template> xterm
Bear in mind that templates are meant to be kept offline, and you should
be particularly careful if you put one online. Any mistake here could
compromise all qubes that use that template.
HTH
unman