Getting 'specififed module cannot be found' when requiring pg from Ruby 3.0

I've installed the latest versions of Ruby and PostGre with their respective installers.

The exact versions are:

• Ruby 3.0.2 with Devkit from: https://github.com/oneclick/rubyinstaller2/releases/download/RubyInstaller-3.0.2-1/rubyinstaller-devkit-3.0.2-1-x64.exe
• PostGreSQL 13.3 from: https://www.enterprisedb.com/postgresql-tutorial-resources-training?cid=437 (which is the version the official page points to).

I've installed the PostGre gem with:

gem install pg -- --with-pg-dir="C:\path\to\PostGre" which installed the pg-1.2.3 gem successfully.

Yet when I do require 'pg' in IRB, I get an error message:

C:/Ruby30-x64/lib/ruby/site_ruby/3.0.0/ruby_installer/runtime/dll_directory.rb:83:in 'add_dll_directory_winapi': AddDllDirectory failed for C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/pg-1.2.3/lib/x64-mingw32 (RubyInstaller::Runtime::DllDirectory::WinApiError)
        from C:/Ruby30-x64/lib/ruby/site_ruby/3.0.0/ruby_installer/runtime/dll_directory.rb:50:in 'initialize'
        from C:/Ruby30-x64/lib/ruby/site_ruby/3.0.0/ruby_installer/runtime/singleton.rb:12:in 'new'
        from C:/Ruby30-x64/lib/ruby/site_ruby/3.0.0/ruby_installer/runtime/singleton.rb:12:in 'add_dll_directory'
        from C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/pg-1.2.3/lib/pg.rb:15:in 'block in <top (required)>'
        from C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/pg-1.2.3/lib/pg.rb:26:in 'rescue in <top (required)>'
        from C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/pg-1.2.3/lib/pg.rb:4:in '<top (required)>'
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:160:in 'require'
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:160:in 'rescue in require'
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:149:in 'require'
        from (irb):1:in '<main>'
        from C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/irb-1.3.5/exe/irb:11:in '<top (required)>'
        from C:/Ruby30-x64/bin/irb.cmd:31:in 'load'
        from C:/Ruby30-x64/bin/irb.cmd:31:in '<main>'
<internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in 'require': 126: Le module spécifié est introuvable.   
- C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/pg-1.2.3/lib/pg_ext.so (LoadError)
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in 'require'
        from C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/pg-1.2.3/lib/pg.rb:5:in '<top (required)>'
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:160:in 'require'
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:160:in 'rescue in require'
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:149:in 'require'
        from (irb):1:in `<main>'
        from C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/irb-1.3.5/exe/irb:11:in '<top (required)>'
        from C:/Ruby30-x64/bin/irb.cmd:31:in `load'
        from C:/Ruby30-x64/bin/irb.cmd:31:in `<main>'
<internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in 'require': cannot load such file -- pg (LoadError)
        from <internal:C:/Ruby30-x64/lib/ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in 'require'
        from (irb):1:in '<main>'
        from C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/irb-1.3.5/exe/irb:11:in '<top (required)>'
        from C:/Ruby30-x64/bin/irb.cmd:31:in 'load'
        from C:/Ruby30-x64/bin/irb.cmd:31:in '<main>'

The main error seems to be the 'specified module cannot be found' (here in French, sorry). How can I fix this?