I keep needing to search to find this, so I’ll write it down.
To download an APK from Android, you need to do the following:
adb shell pm list packages --user 0
adb shell pm path your.package.name
adb pull /data/app/your/path/to/package/foo.apk
If there are multiple APKs (base.apk, arm64_v8a.apk, etc.) it’s an Android app bundle (AAB). You get only the APKs specific to your device.
Incidentally, the publicly accessible data directory for Android apps is in /shared/Android/data/your.package.name/.