You could also try --dns-azure-credentials ~/.secrets/certbot/azure.ini (instead of --dns-azure-config) which should work the same but may have some difference that's relevant.
Personally I didn’t use snap, I used brew on a max to install certbot and then pip to install the azure plugin, they are both in PyPi under slightly different names.
I realise the OP used snap but if they perhaps mucked about with pip too then they could have the wrong version, and that would cause exactly what is described in this thread.