How to make a tun interface with openVPN on LuCI

I have been trying to make a tun interface (to establish a vpn tunnel to my pbx server), but after creating an openVPN instance (on LuCI), i went to the “interface” page and clicked “add interface” but the resulting page does not contain an option for “tun” (under the device menu) although it has an option for “eth”

How do i make a tun interface?

My understanding is that TUN operates in layer3 and eth in layer2

so will an eth interface even work for an openVPN tunnel?

I discovered that after adding “dev-type tun” into my vpn profile, then when clicking “add interface”, the “tun0” option is listed in the device menu

Is that just a label for the interface? or would that tun interface actually be different (technically) from the interface that can be made when choosing the “device-eth” option?

Can anyone answer these 3 questions?