Please refer to my article to know what this code does. https://hesam-kamalan.medium.com/how-to-prevent-the-keyboard-pushes-a-widget-up-on-flutter-873569449927

CustomScrollViewExample.dart

Scaffold(
      appBar: AppBar(...),
      body: WillPopScope(
        onWillPop: onBackClick,
        child: CustomScrollView(
        slivers: <Widget>[
          SliverToBoxAdapter(
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                ...
              ],
            ),
          ),
          SliverFillRemaining(
            hasScrollBody: false,
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.stretch,
              children: [
                Expanded(child: Container()),
                ElevatedButton(
                  onPressed: () {
                    FocusScope.of(context).unfocus(); // Remove Keyboard
                    // Validate Form
                    // Submit the form
                  },
                  child: Text("Submit"),
                ),
              ],
            ),
          ),
        ],
      ),
      ),
    );