Sample configuration to set a machine scoped environment variable

setenvironment.dsc.yaml

# yaml-language-server: $schema=https://aka.ms/configuration-dsc-schema/0.1
# Requires administrator
# Checks for absences of environment variable and sets it if it's not present.
properties:
  configurationVersion: '0.1.0'
  assertions:
    - resource: Environment
      directives:
        module: PSDscResources
      settings:
        Name: 'DSC_EXAMPLE'
        Ensure: 'Absent'
        Value: 'Desired State Configuration'
        Target: 'Machine'
  resources:
    - resource: Environment
      directives:
        module: PSDscResources
      settings:
        Name: 'DSC_EXAMPLE'
        Ensure: 'Present'
        Value: 'Desired State Configuration'
        Target: 'Machine'

Add the code to your hypothetical PS script that does the same thing to enable the other features this does (DSC, for example) then the argument for this is easier to understand. The gist does mention this is a contrived example though, too. More powerful assertions are available and possible which augment the benefit of this approach. See the Winget Configuration docs for more.