Did you change the native VLAN to IoT or just added the tag and left the native VLAN on the switch port set to default? You should be able to change the native VLAN and leave tagged VLANs as “allow all”.
My only other thought is how did you isolate the IoT network and are you able to access other devices from default to IoT?
For someone that re-watches Futurama over and over, it’s hard to get behind any other ending than “Meanwhile” in S10. Meanwhile is just a great end to the series that also carries you back to the beginning.