It's funny how `brew switch` still saves my butt on the regular even though it's been deleted from official Homebrew for ages.

I think most people don’t know, but Homebrew can keep multiple versions of a package installed - if you set HOMEBREW_NO_INSTALL_CLEANUP, when upgrading, the old version will be kept on-disk in an inactive location. `brew switch` was a command you could use to switch which version of a specific version is active, but it was removed awhile back.