My annual subscription automatically renews on March 12, 2022. If I cancel it today, can I continue to use Indesign until March 12, 2022, or is it immediately unavailable?
If you have an annual paid monthly plan you will be able to use it only till March I suppose as the next billing period is till March 12th. Still better to cancel on 1st of March to be totally sure. I am quoting the terms of cancellation below
You can cancel your subscription anytime via your Adobe Account page or by contacting Customer Support*. If you cancel within 14 days of your initial order, you’ll be fully refunded. Should you cancel after 14 days, you’ll be charged a lump sum amount of 50% of your remaining contract obligation and your service will continue until the end of that month’s billing period.
For more details see the following link
If you cancel today, it becomes unavailable today.