It seems that Terminal & SSH both shell into the HA docker container.
I want to configure the base system; how do I access the host OS?
Specifically; I want to configure some vlan network interfaces. I can’t find anywhere inside HA to configure the network environment.
I also want to run another service on the host instance (TP-Link Omada controller).
Alternatively, I try and virtualise the Pi4, and run separate VM’s, but that doesn’t seem very appropriate on a pi.
As succinctly answered by Tinkerer, nothing you would do on the Host OS is supported / “official”.
It’s a “don’t touch” zone as far as support is concerned.