I can confirm that the UiFlow example doesn't work for me either. The block to connect to MQTT seems to be broken or not properly adapted for the SIM7020.
I have the exact problem: Chrome 107.0.5304.110 on Fedora 35. All buttons in the UI (label, button, line, etc) are nonfunctional as well as the "load", "save" etc buttons. UIFlow is completely unusable with Chrome. I can reproduce this in Konqueror also.
in my experience a data SIM (for smartphones, LTE routers, etc.) is not good enough for NB-IoT. You will need a SIM card specifically for NB-IoT plus the NB-IoT service needs to be offered by the provider in your region.