Hi Susan!
How is the /etc/apt/sources.list
file and any files in /etc/apt/sources.list.d/
configured?
It's unlikely to be a firewall issue, however you could try using wget to test that theory, eg:
wget http://azure.archive.ubuntu.com/ubuntu/dists/focal/InRelease
have you tried adding trusted = yes?
deb [trusted=yes] http://azure.archive.ubuntu.com/ubuntu focal main restricted
deb [trusted=yes] http://azure.archive.ubuntu.com/ubuntu focal-updates main restricted