brew update Error: can't modify frozen Array

[choochiya]

Output of brew config

HOMEBREW_VERSION: 5.1.15-40-g8cf7601
ORIGIN: https://github.com/Homebrew/brew
HEAD: 8cf7601ec0b783ab1212143cadb50c3af929826c
Last commit: 57 minutes ago
Branch: main
Core tap: N/A
Core cask tap: N/A
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: ["--appdir=/Users/foo/Applications"]
HOMEBREW_CLEANUP_MAX_AGE_DAYS: 1
HOMEBREW_CLEANUP_PERIODIC_FULL_DAYS: 1
HOMEBREW_DOWNLOAD_CONCURRENCY: 20
HOMEBREW_EDITOR: vim
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_MAKE_JOBS: 10
HOMEBREW_NO_ANALYTICS: set
HOMEBREW_NO_INSECURE_REDIRECT: set
HOMEBREW_USE_INTERNAL_API: set
Homebrew Ruby: 4.0.5 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/4.0.5_1/bin/ruby
CPU: deca-core 64-bit arm_blizzard_avalanche
Clang: 21.0.0 build 2100
Git: 2.54.0 => /opt/homebrew/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.5.1-arm64
CLT: 26.5.0.0.1777544298
Xcode: 26.3
Metal Toolchain: N/A
Rosetta 2: false

Output of brew doctor

Please note that these warnings are just used to help the Homebrew maintainers
with debugging if you file an issue. If everything you use Homebrew for is
working fine: please don't worry or file an issue; just ignore this. Thanks!

Warning: Some installed casks are deprecated or disabled.
You should find replacements for the following casks:
  alacritty
  chromium
  flameshot

Description of issue

brew update always results an error Error: can't modify frozen Array

$ brew update
==> Updating Homebrew...
Already up-to-date.
Error: can't modify frozen Array: []

$ brew update --force
==> Updating Homebrew...
Already up-to-date.
Error: can't modify frozen Array: ["--force"]

$ brew update --quiet
==> Updating Homebrew...
Error: can't modify frozen Array: ["--quiet"]

I am including detailed logs for the 2 errors above produced with --debug --verbose:

• brew-update.log
• brew-update-force.log
• brew-update-quiet.log

---

Maybe related to: https://github.com/orgs/Homebrew/discussions/5507

[choochiya]

$ brew untap buo/cask-upgrade
Untapping buo/cask-upgrade...
Untapped 2 commands (292 files, 538.4KB).

Untapping buo/cask-upgrade seems to resolve the issue.
See buo/homebrew-cask-upgrade#308

[fudaming]

❯ brew trust buo/cask-upgrade
Already trusted tap: buo/cask-upgrade
❯ brew update
==> Updating Homebrew...
Already up-to-date.

trust tap also solve the issue.