The problem I frequently run into is the firewall documentation I get from IoT vendors is nearly always wrong. I can't think of the last time it was correct.
The IoT devices are made of of so many components and the developers only focus on the code they wrote when writing the firewall rules and not everything else.
The last one I did was an IoT device running on top of Windows. The client wanted the Windows devices to be kept patched. And of course, the firewall rules did not include anything to allow Windows Update to run.