Windows sandbox and Powershell : how to make script executable at startup

Question

I followed tutorial to do so :

in wsb:

<LogonCommand>
  <Command>powershell -executionpolicy unrestricted -command "start powershell {-noexit -file C:\scripts\start.ps1}"</Command>
</LogonCommand>

in start.ps1 :

Set-ExecutionPolicy Unrestricted -Force
Set-ExecutionPolicy -scope CurrentUser Unrestricted

but when I try to run a script in sandbox, it still complains script is not executable.