From 2022 IRS form 4684 instructions, p.5, line 5:
From line 5: safe harbor reporting requirements for Form 4684. If you use one of the safe harbor methods provided in Revenue Procedure 2018-08, you must attach a statement to Form 4684 stating that you used Revenue Procedure 2018-08 to determine the amount of your casualty loss. Include the specific safe harbor method used.
