Seems like this problem happened in the past with the level 29 API. https://www.godotforums.org/discussion/25014/google-play-store-release-problem
Following that thread, look for the file
/your game folder/android/build/config.gradle and open it with a text editor, it'll probably list targetSdk and buildTools as 29.
As UnknownUser posted, you might need to mark the "Use Custom Build" option when exporting. When you click export, it'll ask the SDK folder to use and you should point it to the appropriate android sdk build tools folder. On windows, it should be at
Another thing you might need to do is remove that folder android and its contents and reinstall the project's Android Build Template