Hi, you have written about the high download speed. But we have a small one. 27-mobile and 76 computer. We use CDN cloud image upload, we have excellent hosting and very optimized images. But the speed is very low.
In general, our theme is already optimized and doesn’t have too many resources to make your website slow. Most likely, your website performance suffers from the content you have added to your website. It may happen in case of too many plugins, large not optimized images, or other resources. So we suggest you remove unnecessary plugins, install some kind of JS & CSS optimizing plugins like Better WordPress Minify and a caching plugin like WP Super Cache or use WP Rocket for both tasks.
Here is a tutorial that should help you to optimize your website properly https://space.xtemos.com/wordpress-performance-optimization-the-ultimate-guide-in-2021