There are tons of tools which can extract the installed apks from your device. Neobackup and totalcommander for example.

You can use something like this to extract apks https://github.com/AbdurazaaqMohammed/APKExtractor

Google has been pushing developers toward using app bundles instead of APKs. The actual APK you get is specific to your hardware.

The easiest way to get an APK is to ask the developer. If that’s not an option, you can consult a search engine—there are plenty of sites that distribute them (though there’s no way of verifying their integrity).

Do you have permission to upload the APK? What app is it?

You should probably check if it’s already up on APKmirror. It likely is.