Msix not created during Azure DevOps pipeline for WinForms app

I'm trying to create a .msix for a WinForms app using an Azure DevOps pipeline. All the tasks report success, but the artifacts are empty. What am I doing wrong?

variables:
  - template: ../TestVariables.yml
  - group: 'code-signing-variables-group'


parameters:
- name: BuildConfiguration
  displayName: Build Configuration
  type: string
  default: Release
  values:
  - Debug
  - Release

- name: BuildPlatform
  displayName: Build Platform
  type: string
  default: Any CPU
  values:
  - Any CPU
  - x86
  - x64

- name: CleanRepo
  displayName: Clean the repo
  type: boolean
  default: true


# Remove this to enable CI
trigger: none


jobs:
- job: DoItNow
  variables:
    - name: solutionFile
      value: c\MyApp.slnf

  pool:
    name: Default
    demands:
    - msbuild
    - visualstudio

  steps:
  - checkout: self
    clean: ${{ parameters.CleanRepo }}

  - template: ../OurNugets.yml
    parameters:
      BuildConfiguration: ${{ parameters.BuildConfiguration }}
      BuildPlatform: ${{ parameters.BuildPlatform }}

  - task: MSIX.msix-ci-automation-task.msix-packaging.MsixPackaging@1
    displayName: 'MSIX build and package'
    inputs:
      outputPath: '$(Build.ArtifactStagingDirectory)\MyApp.msix'
      solution: $(solutionFile)
      generateBundle: true
      buildConfiguration: ${{ parameters.BuildConfiguration }}
      buildPlatform: ${{ parameters.BuildPlatform }}

  - task: MSIX.msix-ci-automation-task.msix-signing.MsixSigning@1
    displayName: 'Sign MSIX package'
    inputs:
      certificate: 'CodeSigning.pfx'
      passwordVariable: signCertPassword
      timeStampServer: 'http://timestamp.digicert.com'

  - task: PublishPipelineArtifact@1
    displayName: 'Publish Pipeline Artifact'
    inputs:
      targetPath: '$(Build.ArtifactStagingDirectory)'
      artifact: Installer