Any idea why I can't click into the following field to edit it and change the priority. Is it because it is used in a sort?

Is it a textmode field? Are you using a valueexpression? Is it a shared column? Can you go into edit mode and screenshot the column setup?

My guess is that it is a calculated field being auto filled with the either the task's or project's priority or some other value expression.
It could also be that if this is a task report, then maybe that data field is from another object (maybe a project or issue priority rather than a task priority).

If it isn't a calculated field and it is for a sure a task field, consider checking that the task is shared with you to make edits.