[MM3-users] installing a new instance of mm3

Is this document that Brian Carpenter wrote still valid?

https://wiki.list.org/DOC/Howto_Install_Mailman3_On_Debian10

Brian installed my instance. Now its broken. My lists are down. I'm getting nowhere with diagnostics and troubleshooting (which was easier with mailman 2).

I'm considering a new install, hence the question.

Thanks!