Ok if you install cockpit network-manager it installs network manager so there is a conf file in /etc/NetworkManager for the test I changed the section ifupdown to true;
this allows cockpit and network manager control over /etc/network/interfaces this is what you then see in cockpit;
so your network interface is shown there.
Further experimenting do not touch, use add bridge whilst it appears to work it also does want to go off nor be deleted, hence my machine became unusable insert backup usb.
Vlan creation seems to behave but only if I set a static ip, for DHCP it fails to pick up an ip address!!
Quick look at one of TDL's videos and I downloaded radarr this is run in Host according to the video. When you click run to configure the container the default setting is bridge, this is because Ports are enabled by default;
For host disable that setting;
this should allow the container to run in host mode.
However, there does not appear to be any way to add a vlan/macvlan to a container! As yet I have found no information on how this can be done in Cockpits GUI, I'm guessing that this would have to set in cli.