Looks like the Ruby 4.0 Windows build runs from inside the MSYS2

bash.exe

where

/ucrt64/bin/

is on the `PATH`:

$ /c/ProgramFiles64Folder/PuppetLabs/Puppet/puppet/bin/gem.bat env
RubyGems Environment:
  - RUBYGEMS VERSION: 4.0.10
  - RUBY VERSION: 4.0.5 (2026-05-20 patchlevel 0) [x64-mingw-ucrt]
  - INSTALLATION DIRECTORY: C:/ProgramFiles64Folder/PuppetLabs/Puppet/puppet/lib/ruby/gems/4.0.0
  - USER INSTALLATION DIRECTORY: C:/msys64/home/charlie/.local/share/gem/ruby/4.0.0
  - CREDENTIALS FILE: C:/msys64/home/charlie/.local/share/gem/credentials
  - RUBY EXECUTABLE: C:/ProgramFiles64Folder/PuppetLabs/Puppet/puppet/bin/ruby.exe
  - GIT EXECUTABLE: C:\msys64\usr\bin/git.EXE
  - EXECUTABLE DIRECTORY: C:/ProgramFiles64Folder/PuppetLabs/Puppet/puppet/bin
  - SPEC CACHE DIRECTORY: C:/msys64/home/charlie/.cache/gem/specs
  - SYSTEM CONFIGURATION DIRECTORY: C:/ProgramData
  - RUBYGEMS PLATFORMS:
     - ruby
     - x64-mingw-ucrt
  - GEM PATHS:
     - C:/ProgramFiles64Folder/PuppetLabs/Puppet/puppet/lib/ruby/gems/4.0.0
     - C:/msys64/home/charlie/.local/share/gem/ruby/4.0.0
     - C:/ProgramFiles64Folder/PuppetLabs/Puppet/puppet/lib/ruby/vendor_gems
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => false
     - :backtrace => true
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - <https://rubygems.org/>
  - SHELL PATH:
     - C:\msys64\ucrt64\bin
     - C:\msys64\usr\local\bin
     - C:\msys64\usr\bin
     - C:\msys64\usr\bin
     - C:\Windows\System32
     - C:\Windows
     - C:\Windows\System32\Wbem
     - C:\Windows\System32\WindowsPowerShell\v1.0\
     - C:\msys64\usr\bin\site_perl
     - C:\msys64\usr\bin\vendor_perl
     - C:\msys64\usr\bin\core_perl

Fails when run from PowerShell, due to my commenting out a bunch of

.dll

copies.