Try with flutter released apk
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I also came across in this very apk condition when debugging, while in releases around 7-8 mb. This however we could see it in much larger apps, where natively speaking, we need to import many libraries, while with Flutter the work is optimized. So if we assume an app that natively should weigh around 30mb with Flutter it should be similar. What can scare you is in the very basic apps. The important thing however is to optimize the images.
After running flutter build apk --release,
my APK size was 16.2 MB. This APK is called FAT APK which is a single APK that contains binaries for multiple ABIs embedded within it and supports multiple architectures. With flutter build apk --split-per-abi, dart code obsfucates resulting in 3 APK files, size of my app.APK was reduced to 5.6 MB.