I am very confused about this and see the information provided by google is totally inaccurate. Using their own metrics, Page Speed Insights my store is 95 on desktop and 75 on mobile however Shopify ranks me at 25. My store loads quickly, so can only lead me to believe that Shopify is not providing the correct data. I can not rely on Shopify’s suggestions or data when it suggest speeding up the page. I may have to find a better platform
Have you read this thread and other threads on this forum discussing the cloaking method? It makes things quite clear on what might cause a huge diference between a shopify speed score and the score PageSpeed insights gives.
Also, you should study the documentation that google provides on pagespeed metrics so you understand the scoring better. The scoring is based off a global ideal, so if you have 100mb download speed, that'll make a huge diference when visting the site compared to someone from rural india visting the site on their Xiaomi.