您可以维护项目列表的状态，并且可以操作该状态以增加列表的大小，以便网格的大小自动增加。
以下是上述要求的示例：

import 'package:flutter/material.dart';

class WidgetTest extends StatefulWidget {
  WidgetTest({
    Key? key,
  }) : super(key: key);

  // final String title;

  @override
  State<WidgetTest> createState() => _WidgetTestState();
}

class _WidgetTestState extends State<WidgetTest> {
  int present = 0;
  int perPage = 5;

  int _count = 5;
  List<String> productList = [
    "Product 1",
    "Product 2",
    "Product 3",
    "Product 4",
    "Product 5",
    "Product 6",
    "Product 7",
    "Product 8",
    "Product 9",
    "Product 10",
    "Product 11",
    "Product 12",
    "Product 13",
    "Product 14",
    "Product 15",
    "Product 16",
    "Product 17",
    "Product 18",
    "Product 19",
    "Product 20",
    "Product 21",
  ];

  // final originalItems = categoryData;

  var items = <String>[];

  @override
  void initState() {
    setState(() {
      present = present + perPage;
    });
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GridView.builder(
        itemCount: _count + 1,
        gridDelegate:
            SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3),
        itemBuilder: (context, index) {
          if (index == _count) {
            return InkWell(
              onTap: () {
                setState(() {
                  if (_count + 5 < productList.length) {
                    _count += 5;
                  } else {
                    _count += productList.length - _count;
                  }
                });
              },
              child: SizedBox(
                height: 100,
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: [
                    Container(
                      decoration: BoxDecoration(
                        borderRadius: BorderRadius.circular(100),
                        color: Colors.black,
                      ),
                      child: Icon(
                        Icons.add,
                        color: Colors.white,
                      ),
                      height: 50,
                      width: 50,
                    ),
                    const SizedBox(
                      height: 18,
                    ),
                    const Text(
                      "Show More",
                      overflow: TextOverflow.clip,
                      style: TextStyle(
                        fontSize: 16,
                        fontWeight: FontWeight.w600,
                      ),
                    ),
                  ],
                ),
              ),
            );
          }
          return SizedBox(
            height: 100,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                Image.network(
                  "https://firebasestorage.googleapis.com/v0/b/ebuy-1ac5b.appspot.com/o/pngegg%201.png?alt=media&token=fb4dd43b-c537-4471-b81b-e325724f0919",
                  height: 30,
                  width: 90,
                  fit: BoxFit.cover,
                ),
                Text(
                  productList[index],
                  overflow: TextOverflow.clip,
                  style: const TextStyle(
                    fontSize: 16,
                    fontWeight: FontWeight.w600,
                  ),
                ),
              ],
            ),
          );
        },
      ),
    );
  }
}