For anyone who still comes up with this:

From the official Laravel 12 docs

When rendering an exception, Laravel will automatically determine if the exception should be rendered as an HTML or JSON response based on the Accept header of the request. If you would like to customize how Laravel determines whether to render HTML or JSON exception responses, you may utilize the shouldRenderJsonWhen method

use Illuminate\Http\Request;
use Throwable;

->withExceptions(function (Exceptions $exceptions): void {
    $exceptions->shouldRenderJsonWhen(function (Request $request, Throwable $e) {
        if ($request->is('admin/*')) {
            return true;
        }

        return $request->expectsJson();
    });
})