brew update on a macOS executor takes several minutes. I think this is something CircleCI can fix by regularly running this on whatever base image you use. If you did this once a week (or better yet, once a day), running it as part of a CI job should be much quicker.
Note that this was already reported in another post.
While it’s true that setting
HOMEBREW_NO_AUTO_UPDATE=1 does make
brew install run much quicker, it also means it’s not up to date.