How to make a responsive GridView() whose cell sizes change?

I want to create a responsive GridView() but just about everything I find discusses ways to do so that involve adjusting the number of cells in the grid's rows and columns. That's not what I'm trying to do; I'm using a SliverGridDelegateWithFixedCrossAxisCount().

How do you make a GridView() widget that's responsive, with

• a fixed arrangement of columns and rows. As the viewport width and height change, I want the cell sizes to change (rather than the arrangement of rows and columns), and
• cells that appear square, i.e., the childAspectRatio is 1?

My code looks like this:

return GridView.builder(
      physics: const NeverScrollableScrollPhysics(),
      gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 5,
        mainAxisSpacing: 4,
        crossAxisSpacing: 4,
        childAspectRatio: 1,
      ),
      itemBuilder: (context, index) {
        return Container(
          height: cellSize,
          decoration: BoxDecoration(
            border: Border.all(
              color: Theme.of(context).primaryColorLight,
            ),
            color: Colors.white,
          ),
          child: Tile(index: index),
        );
      },
      padding: const EdgeInsets.fromLTRB(36, 20, 36, 20),
      itemCount: 30,
    );

Tile() is a custom widget but it's a Container(). And cellSize does a MediaQuery.of(context) to figure out whether the view's height or width is smaller and select a size to fit.

I spent a lot of time trying to figure this out and, in the end, simply replaced the GridView with rows and columns of Tile objects.