Best way to distribute Flutter application Android & iOS. Best Practices in Flutter Beta Distribution

First, there is no need to submit a different build to either of them. The only thing you need to make sure is if there is a already a build in production mode, the build you are currently submitting must have higher version code than existing.

For Android, you have many options,

Internal test: Quickly distribute your app for internal testing and quality assurance checks.

Closed: Create a closed release to test pre-release versions of your app with a larger set of testers. Once you've tested with a smaller group of employees or trusted users, you can expand your test to an open release. On your App releases page, an Alpha track will be available as your initial closed test. If needed, you can also create and name additional closed tracks.

If you're testing an existing app that you've published before, only users in your test group will receive an update for your closed version.

Open: Create an open release to run a test with a large group and surface your app's test version on Google Play. If you run an open test, anyone can join your testing program and submit private feedback to you. Before choosing this option, make sure your app and store listing is ready to be visible on Google Play.

More information here

For iOS, you have

Internal Testers

Add up to 25 members of your team who have been assigned the Admin, Technical, App Manager, Developer, or Marketer role to test your app. Each member can test on up to 30 devices. Internal testers can access all of your beta builds available for testing.

External Testers and Groups

Invite up to 10,000 external testers using their email address or by enabling and sharing a public link, which creates an open invitation for anyone to test your app. Simply create a group of testers and add the builds you’d like them to test. You can also create multiple groups and add different builds to each one, depending on which features you want them to focus on. When you add the first build of your app to a group, the build gets sent to beta app review to make sure it follows the App Store Review Guidelines. This is the only beta version of your app that requires a full review, and testing can begin once it’s approved.

More information on TestFlight Beta distribution here and here

More information on Crashlytics beta distribution is here. We can upload iOS & Android builds with same application ids.

I used Fastlane to make this possible in the best manner. Please check below.

For iOS Deployment: Beta Distribution & AppStore Distribution

For Android Deployment: Beta Distribution & PlayStore Distribution