Recently Google made it compulsory that all new apps must be uploaded not as .apk files but as .aab files. Till just recently the tool Buildozer was only able to compile your python applications to .apk but recent changes have allowed us to compile to .aab format. This is an instruction set that can be used to create a release .aab.
The new .aab format may be a little confusing. .aab stands for app bundles and consists of a bundle of apk's within it. When you upload an aab to the playstore you are basically uploading a bunch of apk. PlayStore then based on the device that is downloading your application will generate the required apk based on that devices architecture and other parameters.
The introduction of .aab doesn't mean that .apk are no longer useful. .aab are only used for releases where as .apk are still used for testing your application and sharing it with others to directly install(not through the store).
> Note: Test your applications