No. It is not a requirement

Isn’t it documented that Debian is the only supported OS for running the supervised version?

https://github.com/home-assistant/architecture/blob/master/adr/0014-home-assistant-supervised.md

It depends on the VPN. Sometimes there’s a “block local network access” while connected. It could be a client setting or a server setting. Additionally, VPNs are all about routing. So you could run into a problem if you connect to a VPN where the remote network is the same as the IP address of the server you’re trying to connect to.

So if it is that you’re having a conflict between the remote and local networks overlapping, you could change the IP addresses on your local network. It’s probably a good idea not to use the default subnet that your router gives you (like 10.0.0.0 or 192.168.0.0 or 192.168.1.0).

I’ve used both. ZHA didn’t perform as well with my number of devices (58) back when I used it. Zigbee2MQTT seems to perform better for me

I personally like the Zigbee2MQTT add on. And their documentation is great (zigbee2mqtt.io). Also, check out digiblur’s content on Youtube.