I have a top level email address based on my first.lastname@gmail.com ... but it is an unusual name and LinkedIn / google does not find collisions.

The emails say things like "upgrade your trial account now" or "you might be interested in these other products". I have not seen any welcome or request to verify emails.

Unless you’ve got evidence to the contrary: this sounds most likely to be spam campaigns that’s being sent to millions of email addresses, from leaked lists or random generated.

One of the emails is yours

I have evidence to the contrary: there is a real German Shopify account that I never signed up for (I don't even speak German), and these are real emails from Shopify.