The solution in this case (TP-Link TL-WR740N router with OpenWrt 18.06.9 installed) is: there is no way to make simultaniously tagged and untagged VLANs on eth0 (Switch ports), so you cannot use untagged VLAN and tagged VLAN, but: you can use eth1 (WAN port) with "Software VLAN" (just adding eth1.N to bridge), this way you can use eth0 (Switch ports) as a switch, connected to either untagged OR tagged VLAN.
Also, if you have only tagged VLANs, you can use any eth0 port to bridge it with different SSIDs.
https://wiki.mikrotik.com/wiki/Manual:Interface/Wi...
Не путаете с installation = indoor?
Была похожая проблема и решилась этим способом.