Google is my nemesis

[Sprue Cutter]

I suspect, like many others, I'm having issues with Google Merchant, and Google indexing in general.

Problems range from invalid GTIN (Use Global One), yet these are GTIN's supplied by the wholesaler.
Also, promotional overlays on products, (over 3000), that's a lot of work removing all of those, I've used Googles own automatic removal tool, but that doesn't appear to be doing the job.

After 12months of having a site, less than half the products are indexed and searchable.

I's like some help/informed advice to sort this out, I'm 65 yrs old, and I'm wondering if I have enough time left to see a full functioning website.

If it has anything to do with it;
The shopping platform is Shopify (I've read good and bad about it concerning SEO)
testvalleymodels.com.

My main question is, would moving to a platform like Woo Commerce be a better option SEO wise.
The other supplementary questions are;
Is there a definite fix for these issues, and what is it ?