I have almost completed programming my flutter app but now I wonder how I can make my app show real Admob Ads for the app that gets reviewed by Apple/Google (as test-ads are not allowed) if AdMob doesn't allow showing real ads if the app is not already listed on an app store? How can AdMob review whether my app is suitable if I can't even get listed on the app stores since my app can't show real ads.
AdMob Documentation
In order for your app to be reviewed:
Your app must be published. This means that your app is available to users. Your app must be listed in a supported store. This means that your app has a store listing and is available for download from that app store. Your app must be set up correctly in AdMob and linked to a supported store.
Apple Documentation
2.5.10 Apps should not be submitted with empty ad banners or test advertisements.
In my case what I did was, showing some default ads in case ad is loading or some error occurred when loading ad. I used some Amazon ads, added the image they provided and take user to the reference link on ad click. You can also take any other ad service, show default ads, like 4-5 , if the ad do not show due to any case just take any random ad from this 4-5 default ad and show them. In this way Appstore will also not reject your app and after the app is published, you can submit for review to Admob.
Or the alternative is not having ad on your first release. Release the first version without ads. Appstore and Play store are very picky when approving for first release. So publish your first version as simple as possible. And after that you can add ads in 2nd release of your app after the Admob is approved.