This is an accepted solution.
Consider Google Pagespeed/Lighthouse desktop and mobile performance scores as guidance and not a definite metric with respect to your Shopify store. There are many website optimization scanners and all use different metrics and variables to calculate performance.
You can read up about the pros and cons of Google PageSpeed with respect to the Shopify websites, in this article
Additionally, here's another great explanation of Shopify's Speed Score
Now speaking about your store, try scanning your site with a scanner that is tailored to Shopify: https://analyze.speedboostr.com/
It will provide a breakdown of some of the things you can improve on. From what I can see, it could be a good idea to start off with Image optimization.