That's just Google being naughty - every single App uploaded gets that pop-up warning :)
It is any any case to do with Apps that have been coded on other platforms, App Inventor Apps do have some optimisation applied when the APK is built. Of course you should not have any redundant code or unused media in your APK - and Google thinks most APKs do. They are probably right, but their App Bundle format is not supported by App Inventor and does not need to be.
So, safe in the knowledge that you have applied good house keeping in your Project - "mean and lean", you can simply ignore the warning and continue to upload the App.