its actually a complicated process to do in openwrt but it is certainly possible to setup.
assuming you already setup your openwrt router with disabled dhcp and a static IP
first go to Network>>Interfaces, then go click the Devices Tab.
you need to remove all port membership on your br-lan bridge (LAN1,LAN2,LAN3,LAN4)
click save.,… AND DO NOT CLICK THAT SAVE AND APPLY
optional: you can delete the WAN bridge so you can use the WAN port.
create a new device, name it whatever you want in my case i named it ‘vlan’ for simplicity, set the device type to bridge, add the interfaces to bridge (eg LAN1 LAN2, LAN3 LAN4 and WAN if you have deleted the WAN bridge earlier).
click the VLAN Tab and enable VLAN filtering.
now you need to choose which port you want to do all the trunking (eg the ports that will carry all the VLANs that is connected to you managed switch), in my case I use the WAN port as my trunking port so first I need to set my management interfaces first, in my case its the native VLAN1 so enter the VLAN ID 1, tick the local check box, set the trunk port (WAN in my case) as Untagged checkbox and also “Is primary vlan” check, click save.
now go back to br-lan, there should be no member ports on it since we removed it, now click the drop down on bridge ports and choose the newly created interface (in my case its named vlan.1), after that the vlan.1 is added to the bridge, click save, and now you can click save and apply.
in my case I have to plug my ethernet cable to WAN port so I can reach the openwrt adminpage.
after that your openwrt admin page should reachable after the changes, now all you need to do is add the rest of the vlan by going back to vlan device, add a new VLAN ID lets say VLAN ID 30, check the local tick box, set that to trunking port as Tagged. click save.
add a new bridge device, i name it TRUSTED, select the bridge port to newly created vlan (in my case named vlan.30) click save, and save and apply.
now go back to interface tab, add a new interface, select unmanaged as interface type and i named it as TRUSTED_30 add select the TRUSTED device on the list. click save and then save and apply.
now go to you wireless setting add a new SSID, set the interface TRUSTED_30, set the wifi security settings as you like, save, and then save and apply.
test, if it works repeat the same steps from succeeding VLANs you want to add.