When was the last time you watched someone shop in your Shopify store?
When you're working on it everyday you start to become blind to how it works and appears. You already know the shipping information is a link in the footer or you've already dismissed the opt-in popups so they don't appear now.
But to a new customer, they have no idea where anything is. Or, like some stores I've seen, they get hit by half a dozen popups when they first enter.
(That's not an exaggeration either. I've saw one store with at least 11 popups, widgets, or distracting animations all load at once. I have a high-end software development grade computer and even it slowed to a crawl while that store was loading)
In web design some agencies will hire people to use a website and report on how easy, difficult, and confusing specific actions where. Simple things like "find a red shirt and checkout". These usability studies find pages of fixes and optimizations, even for expertly designed websites that follow current best practices.
You could even DIY your own usability test. There are some services online where you hire people to test parts of your site and report back on the process.
Or you can ask a friendly stranger.
You won't get as great of results as if you used professional but you'll be surprised at how effective it'll be. Have 3-5 people go through your store (separately) and try to checkout.
One improvement that always pays off is to learn more about your customers.
The better you understand them, the better you'll be able to help them through your products and services.
If you haven't installed Repeat Customer Insights yet, it can help.
Its analysis will help you find groups of customers so you can begin to understand their actual behavior.