Solution : I choose the "Create Task" Preview action. do not chose the regular 'Create Task' action, then in the Priority section which will be the last input after you hit show all, choose functions input and add this code
if(equals(triggerOutputs()?['body/priority'], 'Urgent'), '1',
if(equals(triggerOutputs()?['body/priority'], 'High'), '2',
if(equals(triggerOutputs()?['body/priority'], 'Medium'), '3',
if(equals(triggerOutputs()?['body/priority'], 'Low'), '4', '3'))))
make sure to substitute the outputs with the answer from your (get form details) on the priority question on the forms. save it and run it and you should have and accurate update of your priority update in planner task. hope this helps