Hi there!
As I also have some problems creating the key inside Construct. I want to share with you and with others with the same problem a tip that allow you to build the apk quite easily.
Requirements:
-Have Android Studio installed (or just the tool apksigner)
-Have already a keystore created (.jks or .keystore)
1.Export your project as "unsigned release apk" (let´s call this GAME.apk)
2.Keep a copy of GAME.apk and also a copy of your keystore (let´s call this MYKEY.jks) in the folder inside the Android Studio, where is the file apksigner.bat. In my case, apksigner.bat is in:
AndroidStudio>sdk>build-tools>27.0.3
So, inside this folder a have a copy of GAME.apk and a copy of MYKEY.jks
3.Run the cmd (command console) and go to the folder where is the apksginer.bat, your GAME.apk and MYKEY.jks.
4.Write this command:
apksigner sign --ks MYKEY.jks --out GAME_SIGNED.apk GAME.apk
when you press enter a message asking for you 2 keystore passwords will appear.
A new file GAME_SIGNED.apk will be created on the folder
Once you do it once, it is a quite fast method.
Cheers! :)