If you still owe taxes on your 2020 return, file your return as soon as possible, even if you can't pay your tax bill right away. The late-filing penalty can be up to 10 times higher than the late-payment penalty, and the longer you wait, the higher the penalty.
On the other hand, if you're getting a refund, you have until April 15, 2024 (or October 15, 2024 if you filed an extension) to file and claim your refund. There is no late-filing penalty in this case, but if you don't file within the allotted timeframe, the U.S. Treasury gets to keep your "donation."