Firstly, switch to classic designer by toggle off 'New designer' flag on the top right corner:

There are issues with file object in new designer. Post switching to classic designer, just retest the flow.
If issue still exists, then you can search output body of get attachment action in dynamic content window and pass to the file parameter:

If this helps & solves your problem, please remember to give a 👍 and accept my solution as it will help others in the future.