Excerpt from `:h shell-powershell`:
To use powershell (on Windows):
set shell=powershell shellquote=( shellpipe=\| shellxquote=
set shellcmdflag=-NoLogo\ -NoProfile\ -ExecutionPolicy\ RemoteSigned\ -Command
set shellredir=\|\ Out-File\ -Encoding\ UTF8
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Use a temporary batchfile for :!, system(), and jobs and run it in cmd.exe.
This bypasses Vim/Neovim issues in Windows and reduces the need to set more options.
Also, s:shellesc_cmd works in a batchfile only.
Set shellredir for system() in Windows
$SHELL sets the default value of 'shell' (see :h 'shell').
This affects shellredir but cmd.exe requires '>%s 2>&1'.