I don’t really know, either. “driver-level VLAN” is the terminology the OpenWRT wiki you linked uses. You went for the strategy at the bottom, with going to the bridge settings and make it add a new interface. Waht I’ve done before, and what that article talks about at the top is, go to the Switch settings, and set the port to the corresponding VLAN, or keep the tags…

https://openwrt.org/docs/guide-user/network/vlan/switch_configuration