Comment by rollcat

What?

You can do a fresh install of an older macOS version whenever you like (you need to enable that option in the rescue system tho).

You can also run older macOS in a VM (the hypervisor framework keeps getting new features that make guest macOS more fully supported).

Name an OS (ok maybe NixOS) that allows you to do clean downgrades out of the box. Also wonder what's gonna happen to your data in e.g. Postgres if you blindly downgrade.