Sure, my configs are below, you might have to adapt them to your needs.

I would recommend to backup your files before changing them.

As I said I let an llm generate them, I basically just put in my current version of the files and stated my intend. I dont know if the bellow config is any way optimal, but for now it works. :P

For the IoT Network I had to disable WWM Mode in the GUI afterwards. Furthermore I disabled the 5ghz band for the IoT network. Otherwise my shelly1 devices wouldnt connect to the new wifi.

The rest of the setup I did according to this Guide: beginners-guide-to-set-up-home-network-using-opnsense

/etc/config/network

config interface 'loopback'
        option device 'lo'
        option proto 'static'
        option ipaddr '127.0.0.1'
        option netmask '255.0.0.0'

config globals 'globals'
        option packet_steering '1'

config device
        option name 'br-lan'
        option type 'bridge'
        list ports 'eth0'
        option ipv6 '0'

# --- Bridge VLAN filtering ---
# VLAN 1 = untagged (native/PVID), VLAN 10 = tagged
config bridge-vlan
        option device 'br-lan'
        option vlan '1'
        list ports 'eth0:u*'

config bridge-vlan
        option device 'br-lan'
        option vlan '10'
        list ports 'eth0:t'

# Management interface (VLAN 1)
config interface 'lan'
        option device 'br-lan.1'
        option proto 'static'
        option ipaddr '10.10.10.10'
        option netmask '255.255.255.0'
        option gateway '10.10.10.1'
        list dns '10.10.10.1'
        option delegate '0'

# IoT interface (VLAN 10) — no IP needed, just bridges WiFi to VLAN
config interface 'iot'
        option device 'br-lan.10'
        option proto 'none'

/etc/config/wireless

config wifi-device 'radio0'
        option type 'mac80211'
        option path 'platform/soc/18000000.wifi'
        option band '2g'
        option channel '1'
        option htmode 'HE20'
        option cell_density '0'
        option disabled '0'

config wifi-iface 'default_radio0'
        option device 'radio0'
        option network 'lan'
        option mode 'ap'
        option ssid 'NerdFi'
        option encryption 'sae-mixed'
        option key 'SuperSecretPassword'
        option ocv '0'

config wifi-iface 'iot_radio0'
        option device 'radio0'
        option network 'iot'
        option mode 'ap'
        option ssid 'NerdFi-IoT'
        option encryption 'sae-mixed'
        option key 'SuperSecretPassword'
        option ocv '0'

config wifi-device 'radio1'
        option type 'mac80211'
        option path 'platform/soc/18000000.wifi+1'
        option band '5g'
        option channel '36'
        option htmode 'HE80'
        option disabled '0'

config wifi-iface 'default_radio1'
        option device 'radio1'
        option network 'lan'
        option mode 'ap'
        option ssid 'NerdFi'
        option encryption 'sae-mixed'
        option key 'SuperSecretPassword'
        option ocv '0'

config wifi-iface 'iot_radio1'
        option device 'radio1'
        option network 'iot'
        option mode 'ap'
        option ssid 'NerdFi-IoT'
        option encryption 'sae-mixed'
        option key 'SuperSecretPassword'
        option ocv '0'

/etc/config/dhcp

config dnsmasq
        option domainneeded '1'
        option boguspriv '0'
        option filterwin2k '0'
        option localise_queries '0'
        option rebind_protection '0'
        option rebind_localhost '0'
        option local '/lan/'
        option domain 'lan'
        option expandhosts '0'
        option nonegcache '0'
        option authoritative '0'
        option readethers '0'
        option leasefile '/tmp/dhcp.leases'
        option nonwildcard '0'
        option localservice '0'
        option ednspacket_max '1232'

config dhcp 'lan'
        option interface 'lan'
        option ignore '1'

config dhcp 'iot'
        option interface 'iot'
        option ignore '1'

/etc/config/firewall

config defaults
        option input 'ACCEPT'
        option output 'ACCEPT'
        option forward 'ACCEPT'

config zone
        option name 'lan'
        list network 'lan'
        list network 'iot'
        option input 'ACCEPT'
        option output 'ACCEPT'
        option forward 'ACCEPT'