Omnia primary router plus OpenWRT DumbAP including Guest Network

My intention is to extend WiFi coverage by adding another AP into the chain.

Internet <---> VDSL <--Eth--> TO (w DHCP) <--Eth--> DumbAP
.............................. / .. \ ............. / .. \
............................. / .... \ ........... / .... \
............................2.4 ..... 5 .........2.4 ..... 5
........................... / \ ..... | ........ / \ ..... |
....................... SSID1 SSID2 SSID1 .. SSID1 SSID2 SSID1

Of course SSID 1 is regular and SSID2 is meant to be GuestWlan with different IP range and Firewall policies.
DumbAP is not as Dumb :wink: it will be VLAN etc capable as it will become another TO, or OpenWRT in my case, configured in accordance to https://openwrt.org/docs/guide-user/network/wifi/dumbap.
My assumption is there will be necessary to do additional VLAN and establish trunk connection between TO and DumbAP.
Is there any recommended way to create VLANs under 5.x branch? It was rather “easy=I understand” under 3.x branch; however I am confused under 5.x what should be configured and the configuration should survive regular Omnia updates.
Here, on the forum I have just found https://forum.turris.cz/t/2x-omnias-one-as-router-second-as-ap/5763 which has no answer at all and is 3 years old and TOS5 VLANs: https://forum.turris.cz/t/tos5-vlan-nightmare/13175.
The most promising is following thread: https://forum.turris.cz/t/total-obsolete-vlan-documentation/13121/25 ; however some common approach would be better as different setup will lead into future nightmare.

I have a comparable use-case with a gluon-router and a turris mox in my flat.

On the mox I’m using a tagged (vlan-id 42) and an untagged VLAN on LAN-Port 6. I achieved this by adding option ifname <other ports> lan6.42 to the bridge interface called lan and option ifname <other ports> lan6 to the guest interface in the config file /etc/config/network.

On the gluon-device I added another wifi and an additional interface for the tagges vlan and bridged (?) those two.

Thanks, finally I found the trick to add VLAN manually and surprisingly it is propagated as expected… Anyway I am not sure why Turris missing Switch option. I am owning two TP-Links (N900 and Archrer C7). The first one utilizes DSA under OpenWRT like sharm and other one is having exactlz same switch chip like Omnia also working as expected both being on 19.07.4