I have been following the guide available here:
I think they are omitting a rather important issue regarding host firewalls.
For example, on Centos 8 I allow docker0 with the following command:
firewall-cmd --permanent --zone=trusted --add-interface=docker0
This works with the default bridge. When you create a new network, this creates a new network interface.
The guide should remind that this interface also needs to be considered by the host firewall. I have been troubleshooting for 1 hour until I realised that by creating an additional docker network, it was no longer using the default docker0 and now using a new br-xxxxx interface.
This was easily fixed by
firewall-cmd --permanent --zone=trusted --add-interface=br-xxxxx
I hope this avoids someone else the wasted time.