Can I have android games using the same leaderboards and achievements in google play games

Question 1

Absolutely can use the same leaderboard(s) and achievements..

In your Google Developer Account, under the Game Services link, you setup a Game. (with all the Leaderboards and Achievements you want to have available for any/all versions of your Game)

enter image description here

Then, under each Game, you then get to link Apps up to the Game. The linked apps can be up to 20 applications in total, covering Android/iOS/Web applications. The linked apps could all be 20 Android if you want, or 10 Android/10 iOS, or any combination of the three. Any of those can be free or paid.. .and you could have multiple leaderboards, with each App deciding which leaderboard(s) to pick from and to display/update. If you want them to all share the same leaderboard(s), that's fine.. .if for some reason you want to have a leaderboard for each specific platform/app version that would be fine too, as well as maybe having an overall leaderboard for All of your different Apps. (from below, you can see I have three different apps linked to the dice game, and all three are android, and all are ready to publish, and they all use the same leaderboards/achievements and use the Room services)

enter image description here

The Google Leaderboard Tutorial doesn't cover this quite to the detail that you were probably looking for, and hopefully this shows how to setup multiple apps/platforms for one game a little clearer and with more confidence that it does do exactly what you are looking at implementing.

Question 2

Google play Services Leaderboard Tutorial check Leaderboard, Achievement, cloud save examples

Question 3

Unfortunately, this doesn't quite work without some modification by players on the iPhone side.
There's a few things that have to happen to even get the leaderboards to show up somewhat correctly on the iPhone side.

On the Google Play Developer Console, you need to go to your Game services and go to the Leaderboards page. Select the leaderboard in question and review the properties. In order to make sure that the iPhone users can see anything on the leaderboards, the property Enable tamper protection needs to be set to off.

This allows the iPhone app user to see the scores on the leaderboard. However, even with this, that iPhone user will not be able to post to the public leaderboard. When the iPhone app user invokes the show leaderboard methods, the leaderboard UI will show up and offer the choice between Social and All. Unfortunately, the default for the iPhone user is that their scores will not be present on the All list. They will, however, have their scores presented on the Social list.

In order to permit the scores to be shown on the All leaderboard, the iPhone user must make sure their permissions are set so they will allow public exposure of their activities.

I have read that in some cases, this is permitted by invoking Game Center prior to running the target app. I've also read that the personal profile's privacy settings in Game Center needs to make sure that the user's profile settings are public. I think that depends on which version of the OS you currently have on your iPhone.

Question 4

You can also have a look at V-Play Engine for qt-based apps and games. It comes with many components to make mobile development easier.

You can also add leaderboards and user profiles to your application with a few lines of code:

import VPlay 2.0
import VPlayApps 1.0
import QtQuick 2.9

App {

 // app navigation
 Navigation {
   NavigationItem {
     title: "User Profile"
     icon: IconType.user
     NavigationStack {
       initialPage: socialView.profilePage
     }
   }

   NavigationItem {
     title: "Leaderboard"
     icon: IconType.flagcheckered
     NavigationStack {
       initialPage: socialView.leaderboardPage
     }
   }
 }

 // service configuration
 VPlayGameNetwork {
   id: gameNetwork
   gameId: 285
   secret: "AmazinglySecureGameSecret"

   // increase leaderboard score by 1 for each app start
   Component.onCompleted: gameNetwork.reportRelativeScore(1)
 }

 // social view setup
 SocialView {
   id: socialView
   gameNetworkItem: gameNetwork
   multiplayerItem: multiplayer
   visible: false // we show the view pages on our custom app navigation
 }
}

See here for more information: https://v-play.net/cross-platform-app-development/how-to-add-chat-service-and-cross-platform-leaderboard-with-user-profiles-to-your-ios-or-android-app#add-leaderboard-with-user-profiles