I am not able to run a file as "run as workflow" nor "run with databricks connect" when I choose serverless run on my paid account.  However I can perform this action in my free edition account . 
See error : 
pyspark.errors.exceptions.connect.SparkConnectGrpcException: PERMISSION_DENIED: Cannot access Spark Connect. (requestId=e6437897-ac03-4c06-b7a6-5b25ee676d03)