I called Asia Miles and this is their policy now:

If you have miles expiring in 2021, 2022, & 2023, you have to redeem an air ticket and cancel after the miles expiry date and the miles will be extended for another year. Eg: if your miles expire on 31 Jan 2022, your travel date is May 2022, you cancel in March 2022, once you cancel, your miles will expire on 31 Jan 2023. If you book another redemption ticket and you cancel again after 31 Jan 2023, your time based miles will be converted to the new activity based miles. In other words, only in 2023, Asia Miles will convert your time based miles will be converted to the new activity based miles. If you have miles expiring in 2022 and 2023, you have to book a redemption ticket 2 times.

To use 12,000 Asia Miles as the cancellation fee, you must have the 12,000 miles in your account, cannot deduct from the miles that is going to be refunded. To get free cancellation, either the airline change the timing of flight or cancel the flight.