How can I sign my app? .pem vs .jks

I originally was using expo:build, and my app signing was working fine. Now I’m trying to use eas build, and nothing is working.

I got the “Your app is signed with the wrong key” error when trying to submit it to the Play Store.

I looked around and learned about contacting google to change the keystone on their end.

So I thought “ok cool, I’ll just change it to the old keystore. Hooray, everything will be good now!” Wrong! It didn’t work, because the only Keystore I could export was a .jks and the people at google would only take a .pem file.

So I found other docs that mention .pem files
and I ran that. Submitted the .pem to google, they updated my keystore with that. Everything should be fine now right? WRONG!
Now eas is still signing them with the oldi .jks keystore, not the new .pem one.

“Well” I said to myself. “Maybe there’s a way to upload the .pem file to eas build so that my app bundles can be signed with it.” It was a good idea, but no. EAS has a guide on using local credentials, but wouldn’t you know it, it only takes .jks files. No support for .pem files.

Would some kind soul please explain to me (like I’m 5) how to sign an android app bundle using my .pem file? Or at least please tell me what I’m doing wrong?