Demonstration for changing nested Navigator size depending on current page.

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MainApp());
}

class MainApp extends StatelessWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Scaffold(
        body: SingleChildScrollView(
          child: Column(
            children: [
              _SizedContent(height: 300, color: Colors.red),
              _SizedContent(height: 200, color: Colors.blue),
              _SizedContent(height: 500, color: Colors.green),
              _SizedContent(height: 300, color: Colors.yellow),
              _SizedContent(height: 200, color: Colors.purple),
              _SizedContent(height: 100, color: Colors.orange),
              _SizedContent(height: 50, color: Colors.brown),
            ],
          ),
        ),
      ),
    );
  }
}

class _SizedContent extends StatelessWidget {
  const _SizedContent({required this.height, required this.color});

  final double height;
  final Color color;

  @override
  Widget build(BuildContext context) {
    return DefaultTextStyle(
      style: const TextStyle(fontSize: 32, fontWeight: FontWeight.bold),
      child: Navigator(
        onGenerateRoute: (settings) {
          return MaterialPageRoute(
            builder: (c) => GestureDetector(
              onTap: () {
                Navigator.of(c).push(
                  MaterialPageRoute(
                    builder: (c) => GestureDetector(
                      onTap: () {
                        Navigator.of(c).pop();
                      },
                      child: Container(
                        height: height * 2,
                        color: color.withAlpha(180),
                        child: Center(child: Text('Second Page!')),
                      ),
                    ),
                  ),
                );
              },
              child: Container(
                height: height,
                color: color,
                child: Center(child: Text('First Page!')),
              ),
            ),
          );
        },
      ),
    );
  }
}