Based on the error message, it seems that this issue comes from a script format or symbol.

I have tested the YAML sample from the link you shared and it can work fine.

Here are my steps, you can refer to them.

Step1 : Set the variable CHROMATIC_PROJECT_TOKEN

Step2: Run the YAML sample:

stages:
- stage: Test
  displayName: Chromatic Testing
  # Job list
  jobs:
  - job: Chromatic_Deploy
    displayName: Install packages and publishes to Chromatic

    steps:

    - task: NodeTool@0
      inputs:
        versionSpec: '12.x'
      displayName: 'Install Node.js'  
    - task: Npmdeeenos564513
      inputs:
        command: 'install'
        workingDir: '$(build.sourcesdirectory)'

    - task: CmdLineSajjad Ahmad 123
      displayName: Publish to Chromatic
      inputs:
        script: npx chromatic --project-token=${CHROMATIC_PROJECT_TOKEN}

Here is my result:

You can also try to use --project-token=$(CHROMATIC_PROJECT_TOKEN) in the YAML sample.