I hit a wall here also, crafting a sys-net template from a slightly trimmed debian-12-minimal base.
journalctl -b provided the clue:
...
<timestamp> sys-net NetworkManager[531]: <error> [....] device (wls6f0): Couldn't initialize supplicant interface: Failed to D-Bus activate wpa_supplicant service
...
Fixed with:
$ apt install --no-install-recommends --assume-yes wpasupplicant
So, for my machine, the complete list of required packages:
firmware-iwlwifi
qubes-core-agent-networking
qubes-core-agent-network-manager
wpasupplicant