You don’t need to make a new bridge, just configure VLANs on the existing bridge. In one go, configure VLANs on the bridge and change the LAN interface to br-lan.1 (or whatever you chose for the LAN vlan), then make more interfaces for the additional VLANs.
This currently leads to a bug in OpenWRT, which leads to lock out of the system, but I still tested via a separately configured port so.
Unfortunately this does not change the behavior, as soon as the default LAN adapter is set to e.g. untagged lan0.1, the network ports in the bridge are completely disabled.
Now and then this works, but leads to very strange errors, like web becomes very slow, webinterface shows errors when opening, etc,…
In addition, the “Reforis webinterface”, the LAN interface can no longer configure.
Sorry, I forgot exactly what the default configuration looked like.
You want a single bridge interface (in Network > Interfaces > Devices) that covers all the ports, and then make VLAN devices off of those, and then make the LAN interface use a VLAN device.