You received an "Unoptimized APK" warning while uploading your Android app APK file onto the Google Play Store. This is an App Bundle's related warning which you can ignore and proceed with your app's submission/publishing.
While uploading your Android app APK file onto the Google Play console you received the following warning:
This APK results in unused code and resources being sent to users. Your app could be smaller if you used the Android App Bundle. By not optimizing your app for device configurations, your app is larger to download and install on users' devices than it needs to be. Larger apps see lower install success rates and take up storage on users' devices.
Use the Android App Bundle to automatically optimize for device configurations, or manage it yourself with multiple APKs.
This warning appears because the APK does not use App Bundles. App Bundles is Android's new publishing format, which is not mandatory. Google tends to show these warning messages for apps that were built using 3rd-party templates like BiznessApps.
Other warnings may be included, depending on your app's configuration. See the Two Warnings Related to a Deobfuscation File and Debug Symbols article for other examples of App Bundle-related warnings.
"Unoptimized APK" warning message can be safely ignored. This would not stop the upload process from completing the new version rollout.
You can click on the Close button, and continue with your APK update.
After closing the Warning message, you should be able to continue with the APK upload process.