How to have widgets outside the app using flutter and kotlin?

This is known as a Draw Over Other apps.

This feature is not available in the iOS probably that's the reason flutter doesn't has this feature or official package for it.

But to achieve this feature in your application you can write up some PlatformChannels.

This permission allow you to draw on top of everything.

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>

Allows an application to open windows using the type TYPE_SYSTEM_ALERT, shown on top of all other applications. Very few applications should use this permission; these windows are intended for system-level interaction with the user.

Constant Value: "android.permission.SYSTEM_ALERT_WINDOW"

This code can also help you out to achieve this.

You can also check out springy-heads library by Flipkart-Incubator too.

Hello in this case you are searching for PlatformChannels You can review the documentation here: https://flutter.dev/docs/development/platform-integration/platform-channels or if you want i have a little post about this on my website: http://fjbatresv.com/flutter-tambien-habla-nativo/ (Select your language on the top of the post.)

Apart from restriction that it won't work on IOS, there is a plugin in flutter called System Alert Window, which does the same

It shows Truecaller like overlay window, over all other apps along with callback events