Thanks so much for your help.
I followed your steps and managed to switch one of my boxes from CentOS Stream back to CentOS Linux 8 successfully. I was lucky that I did not have the login issue as you had experienced so I did not have to do those last steps.
One note though that I had to update the link in the first wget from http://mirror.centos.org/centos/8/BaseOS/x86_64/os/Packages/centos-linux-release-8.3-1.2011.el8.noarch.rpm to http://mirror.centos.org/centos/8/BaseOS/x86_64/os/Packages/centos-linux-release-8.4-1.2105.el8.noarch.rpm
That’s the only change I made.
Once again thanks you, you have saved my day.