Using the Google Search Console I ran the Core Web Vitals and it has brought back warnings for both mobile and desktop on over 400 URLs which is a bit worrying. The two issues are shown in the first screenshot and are CLS and LCP issues. I understand from online research what these are, but how to fix the issues... no idea.
I then had a look at Page Speed insights which also highlights quite a few issues here.
Can anyone at Shopify shed any light on how I can improve or fix this as I could not find anything on the forum or in the help section.
Are you sure Search Console is showing you the metrics for the AMP version and not the regular one?
My recommendation is to switch your site to AMP Standard mode, and then work on resolving any AMP compatibility issues that might pop up. Then you should see much better values.
https://webmasters.googleblog.com/2020/05/evaluating-page-experience.html - hope this link will help you.
Please check at app section in your store , Is there any amp related app?