Why isn't SemRush properly crawling my website?

Shopify can’t do this type of work for, for issues with third party services you need to go that third parties support or forums.

Beyond that make sure the sites robotx.liquid doesn’t block semrush boths.

That your sitemap is working, etc.

And research writings on doing seo audits against shopify sites.

https://www.shopify.com/blog/technical-seo-audit