When all you have is a hammer, everything looks like a nail.

yes, docker is a great solution nowadays for this problem, but it wasnt always like that. In PHP land there is a tool called Laravel Valet, which relies heavily on homebrew and lets you switch PHP versions on the fly directly your system. I just remember how much of a pain it was to set up because of homebrew's unnecessary restrictions and deprecations. But once done it worked quite well.

so don't use brew at all? Great, what else should we not use?

It works until PHP officially EOLs the version. Then brew stops supporting it and you have to install some finicky 3rd party taps/repos to get the older versions. A huge pain...

In the real world there are still apps running PHP 7.4 and even older!