Error: The apk for your currently selected variant (Unknown output) is not signed. Please specify a signing configuration for this variant (debug)

This occurred to me too, this might happen because the default signing configuration is modified after upgrading to Gradle 7.0.0. You can fix this without downgrading the Gradle. To do this,

go to File menu > Project Structure. Step Reference Image 1

then go to Modules section Step Reference Image 2

then head to Default Config tab Step Reference Image 3

Scroll down to Signing Config then click dropdown Step Reference Image 4

select $signingConfigs.debug from the drop-down list Step Reference Image 5

Click APPLY then OK then Run your app again.

That SOLVED the issue for me. Hope it works for you too.

What worked for me was to add the following on the app level build.gradle (For the 'release' variant in this example):

android{
   
   signingConfigs {
       release {
           storeFile file("path to your keystore file")
           storePassword "your store password "
           keyAlias "your keystore alias"
           keyPassword "your key password"
       }
   }

   buildTypes {
       release {
           ...
           ...
           signingConfig signingConfigs.release
       }
   }   

}

I was getting the same issue and came across your posts. Fortunately, I was able to fix it. Follow the step below: Build Variants (lower-left corner) > Active Build Variant > change it back to Debug

The problem occurs if Android Gradle Plugin (AGP) is higher than 7.0.0-alpha08. So downgrading to 7.0.0-alpha08 solves the problem. By doing so, you must also downgrade to Android Studio Arctic Fox (2020.3.1) Canary 8 because later versions require their corresponding AGP or the latest one. I'm not happy with the downgrade solution. But this is the only way for the tests to run at the moment.

Android Studio Archives

make sure you are not using signingConfig in app level build.grade or try with invalidate caches/restart option from file option in menu bar.

This is now fixed in the latest preview build of Android Studio (2020.3.1 Canary 15), using AGP version 7.0.0-alpha15!

In app level build.gradle file add

defaultConfig{
    ...

    signingConfig signingConfigs.debug
}

inside defaultConfig block