website is sluggish even thou the speedtest is ok

I purchased the WoodMart theme for this website: https://alzoo-vet.com . I am using WPRocket and CloudFlare, and I have also done all the setups recommended in this article: https://xtemos.com/wordpress-performance-optimization-the-ultimate-guide-in-2021/. The pageSpeed tool gives me an upper 70s performance for mobile devices, which is fine. But once you click on adding to cart, checkout, update the quantity, remove..etc, the spinner keeps on loading for seconds ..sometimes even over 10 seconds for a simple request. I need to know what we can do and where the issue is, because this is clearly a significant problem for an e-commerce website. And even if the pageSpeed tool tells me it’s OK, the overall website load is sluggish and unacceptable. Looking forward to any help you can provide … thank you.