Unsupported special dependency :x11

[grbman]

Hi,
I'm getting Unsupported special dependency :x11 when trying to tap dholm/homebrew-sdr.
I'm running MacOS 12.1 on a M1 Mac.
Output:

brew tap dholm/homebrew-sdr
==> Tapping dholm/sdr
Cloning into '/opt/homebrew/Library/Taps/dholm/homebrew-sdr'...
remote: Enumerating objects: 441, done.
remote: Total 441 (delta 0), reused 0 (delta 0), pack-reused 441
Receiving objects: 100% (441/441), 120.77 KiB | 1.01 MiB/s, done.
Resolving deltas: 100% (269/269), done.
Error: Invalid formula: /opt/homebrew/Library/Taps/dholm/homebrew-sdr/multimon-ng.rb
multimon-ng: Unsupported special dependency :x11
Error: Cannot tap dholm/sdr: invalid syntax in tap!

And here's my brew config:

brew config
HOMEBREW_VERSION: 3.3.15
ORIGIN: https://github.com/Homebrew/brew
HEAD: d603fd6426ddae27327bb51afb085653eb2d84a7
Last commit: 6 days ago
Core tap ORIGIN: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 0248e7af0605103a72e0725f964ffaec51dc8716
Core tap last commit: 2 hours ago
Core tap branch: master
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_CORE_GIT_REMOTE: https://github.com/Homebrew/homebrew-core
HOMEBREW_DISPLAY: /private/tmp/com.apple.launchd.HPADfuyQCR/org.xquartz:0
HOMEBREW_MAKE_JOBS: 10
Homebrew Ruby: 2.6.8 => /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby
CPU: 10-core 64-bit arm_firestorm_icestorm
Clang: 13.0.0 build 1300
Git: 2.34.1 => /opt/homebrew/bin/git
Curl: 7.77.0 => /usr/bin/curl
macOS: 12.1-arm64
CLT: 13.2.0.0.1.1638488800
Xcode: 13.2.1
Rosetta 2: false

[Ow1e]

I'm getting the same issue on my 2017 Intel Mac too

[hexsecs]

same..

==> Tapping dholm/sdr
Cloning into '/opt/homebrew/Library/Taps/dholm/homebrew-sdr'...
remote: Enumerating objects: 441, done.
remote: Total 441 (delta 0), reused 0 (delta 0), pack-reused 441
Receiving objects: 100% (441/441), 120.77 KiB | 1.23 MiB/s, done.
Resolving deltas: 100% (269/269), done.
Error: Invalid formula: /opt/homebrew/Library/Taps/dholm/homebrew-sdr/multimon-ng.rb
multimon-ng: Unsupported special dependency :x11
Error: Cannot tap dholm/sdr: invalid syntax in tap!

HOMEBREW_VERSION: 3.4.11
ORIGIN: https://github.com/Homebrew/brew
HEAD: 30e3d8883cde265cbc16ff94b49a3ac14137590e
Last commit: 2 weeks ago
Core tap ORIGIN: https://github.com/Homebrew/homebrew-core
Core tap HEAD: 2f008323193f636d32c4a970caa9e8b528c6c430
Core tap last commit: 60 minutes ago
Core tap branch: master
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_CORE_GIT_REMOTE: https://github.com/Homebrew/homebrew-core
HOMEBREW_MAKE_JOBS: 10
Homebrew Ruby: 2.6.8 => /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby
CPU: 10-core 64-bit arm_firestorm_icestorm
Clang: 13.1.6 build 1316
Git: 2.36.1 => /opt/homebrew/bin/git
Curl: 7.79.1 => /usr/bin/curl
macOS: 12.3.1-arm64
CLT: 13.4.0.0.1.1651278267
Xcode: 13.4
Rosetta 2: false