VLAN, subnet and interface configurations

[c0nnected]

Hi,
I'm trying to setup my VLAN, subents and interface, but I feel like I'm missing something.
I have following interfaces:
WAN
LAN
OPT1
OPT2
OPT3
OPT4
OPT5
OPT6
and I have a Vlan 100 with address 10.100.100.1 where parent interface is LAN. How Can I assign this vlan to other interfaces like OPT1 and OPT2? On typical network device like Cisco or Arista I can easily create vlan interface and then assign vlan to any number of interfaces, but this fundamental function seems to be missing here.

[Patrick M. Hausen]

OPNsense is not a switch but a router. There is no forwarding plane that can connect ports to a VLAN. VLAN interfaces are just tagged subunterfaces. The parent interface is intended to be conncted to a switch.

You can emulate a switch with a bridge interface. But it's not really recommended.