Making all VMs use UpdatesProxy

Is there a downside to doing this? For VMs that use a netvm, that is.
It would probably be best to exclude VMs that are airgapped.

TemplateVMs connect to while StandaloneVMs and AppVMs connect to

I tried following a thread on Reddit but didn’t achieve the same result.

I don’t think there’s any downside - particularly not if you use a
caching proxy in place of tinyproxy, and use that as netvm for the qubes
you are interested in.
Except of course, that the proxy setup will circumvent any firewall
rules you have set. The tinyproxy package no longer filters
destinations out of the box.

If you install the necessary packages in an airgapped machine you can
still use the proxy - provided it’s some variant of Debian, Ubuntu,
Centos, Fedora, Arch.

I don’t know why you would have a different port but that’s your call.