How to fix "not valid signature" error in google play?

Question

Google Play

Made an update to the app. When loading, it was required to set the target api 29 and at the same time migrate that android x. It seems to have coped, the studio does not swear. But if you compile .aab and upload it to the play store, it says "not a valid signature Error from apksigner tool: .". What is it? How to fix it?
PS if you compile .apk, then everything is fine. What is their difference? Why not use .apk instead of the recommended .aab all the time?