While the pcWRT router firmware does support VLAN creation on the router itself, out of the box it does not support incoming tagged VLAN traffic. You need to log in the router shell to edit the switch configuration manually. Doing so will mess up the UI for VLAN assignments on the Network Settings page, but as long as you don’t update network settings from that page again you should be fine.
More info on manually setting up VLANs is available here: https://openwrt.org/docs/guide-user/network/vlan/switch_configuration
