You would have to report the rent in 2021. Since there was no rental usage, you can't deduct expenses or depreciation.
Advance rent is any amount you receive before the period that it covers. Include advance rent in your rental income in the year you receive it regardless of the period covered or the method of accounting you use.
If you have any personal use of a vacation home or other dwelling unit that you rent out, you must divide your expenses between rental use and personal use.
Rental income and expenses