結論
$ brew update
実例
$ brew --version
Homebrew 4.0.24-26-g8d9aa90
$ brew update
==> Downloading https://ghcr.io/v2/homebrew/portable-ruby/portable-ruby/blobs/sha256:f7be167f7ac4f296b9f4c5874ceeea4aafd9999c3c7f2b0378cae7dd273e2322
######################################################################## 100.0%
==> Pouring portable-ruby-3.1.4.x86_64_linux.bottle.tar.gz
==> Homebrew collects anonymous analytics.
Read the analytics documentation (and how to opt-out) here:
https://docs.brew.sh/Analytics
No analytics have been recorded yet (nor will be during this `brew` run).
==> Downloading https://formulae.brew.sh/api/formula_tap_migrations.jws.json
################################################################################################################# 100.0%
Updated 4 taps (dart-lang/dart, leoafarias/fvm, homebrew/core and homebrew/cask).
==> New Formulae
（中略）
You have 1 outdated formula installed.
You can upgrade it with brew upgrade
or list it with brew outdated.
==> Downloading https://formulae.brew.sh/api/cask_tap_migrations.jws.json
################################################################################################################# 100.0%
$ brew --version
Homebrew 4.2.20
公式ドキュメント
docs.brew.sh
