Yarn that was installed via Scoop doesn't install global packages properly.

TL;DR: Suggested hot fix workaround

If you are a Scoop user and want to fix the bug ASAP than you may add %LOCALAPPDATA%\Yarn\config\global\node_modules\.bin to your PATH environment variable.

Test scenario:

I have Windows 10 desktop with fresh Scoop installed. After that:

scoop install nodejs yarn
yarn global add http-server

The last command generated file $env:HOMEPATH\scoop\apps\yarn\current\bin\http-server.cmd.
Scoop previously added this file's folder to $env:PATH.
This file contains only 1 non-empty line:

@"%~dp0\..\..\..\..\AppData\Local\Yarn\config\global\node_modules\.bin\http-server.cmd"   %*

The command http-server returns following output:

The system cannot find the path specified.

Bug source

I've tried to find the bug reason. So I've edited the file and added 1 more ..\ right before AppData:

@"%~dp0\..\..\..\..\..\AppData\Local\Yarn\config\global\node_modules\.bin\http-server.cmd"   %*

The resulting file works.

The same issue is reproduced with any global Yarn package. We have to figure out if this a Scoop or Yarn issue.