Can't use my old Key to sign an App with Air

I have a few Apps on Google Play, and I'm having problems since I migrate to Animate 2020. I can't use some of my keys to send upgrades to Google Play. I still can sign them using the old Animate 2017, but in this way I cant send it in the required 64bits code.

I think the problem is that the certificates are 1024 and not 2048, but I still need to use the same old one, as is it an upgrade.

How can I solve this?

Thanks !