Loop through dynamic template parameters in Azure devops YAML

I want to perform some actions (publish) on an array of string which are passed as parameter. The thing is, this parameter is dynamic :

# pipeline.yml

- job: MyJob
    pool:
      [...]
    steps:
      - pwsh: |
          $affected = ['app-one', 'app-two'] # Here I hardcoded the array but in my real code this is set dynamically
          Write-Host "##vso[task.setvariable variable=affected;isOutput=true]$affected"
        name: setAffected
        displayName: 'Settings affected'

- template: ./build.yml
  parameters:
    affected: $[ dependencies.Affected.outputs['setAffected.affected'] ] # Here I pass the array of string to the template

# build.yml

parameters:
  affected: ''

jobs:
  - job: Build
    condition: succeeded('Affected')
    dependsOn: Affected
    pool:
      [...]
    variables:
      affected: ${{ parameters.affected }}
    steps:
      - ${{each app in $(affected)}}:
          - pwsh: |
              Write-Host "${{app}}"
      - ${{each app in parameters.affected}}:
          - pwsh: |
              Write-Host "${{app}}"

Neither of ${{each app in $(affected)}} or ${{each app in parameters.affected}} work... How can I manage to execute some actions on each of my array item?

Thanks