when we leave the EU we will still need to comply with the regulations as the EU has made it worldwide somehow.
Easy there! If you do business in the EU, and therefore handle the data of EU citizens, this applies to you. If you are located outside the EU, and are dealing with non-EU citizens' data, it doesn't apply to you. If you need to implement anything new to meet GDPR, it should be a superset of data-protection requirements anywhere else in the world, and you can handle everything the same way. Now, if you're physically located outside the EU, I doubt they'll have much leverage with you, even when dealing with EU citizens. If you're a small shop, and make a reasonable effort to protect personal data, frankly I doubt they'll bother coming after you. They've got bigger fish to fry with Amazon, Google, etc.
Has any store owner seen a sensible easy to understand website that explains how this may affect store owners, or like me have you never heard about this until now.
From a very quick scan of the Wikipedia article, it sounds like mostly common-sense data protections. I don't see anything that says the Data Protection Officer has to be a discrete person -- it can be another hat you wear (president, web guru, shipping clerk, bottle washer, DPO,...). People can request that their data be moved to another system, which is not applicable if you don't run elsewhere (what are they trying to accomplish here?). People can request to be forgotten (you erase their account information upon request, where that doesn't conflict with statutory data retention requirements or good accounting principles). Data breaches have to be reported to the appropriate authority. Customers have to explicitly consent to having data collected (it should be enough to add "By providing this information, you are consenting to our collecting it" to registration and PWA pages), and there are restrictions on collecting information from children. There are some privacy provisions which anyone handling personal data should already be implementing, at least for the type of data an online shop would hold. There may be some extra i-dotting and t-crossing to be done, but what else is new?