For unexplained reasons, ^13 is the code that has to be used in the Find What box to search for Paragraph Marks when the “Use wildcards” option is ON. Have a look at
https://support.office.com/en-SG/article/replace-text-using-wildcards-5cda8b1b-2feb-45a6-af0e-824173d3d6e4]Use codes to find letters, formatting, fields, or special characters. However, and as far as I am aware, both ^13 and ^p can be used in the Replace With box, irrespective of whether the “Use wildcards” option is ON or OFF. I personally use ^13 in both boxes not to complicate things needlessly.