Your store has two faces
Where did you last look at your store? Your laptop, probably. Where did your last customer look at it? In bed. On a phone. One thumb. 11pm. Half watching something else.
"Mobile-friendly." There's a phrase. Friendly is a low bar. My landlord is friendly. It means the site shrinks to fit the phone. Nobody said it would make sense there. The hero that's gorgeous at 1440 pixels wide is a stack of orphans at 390. The 3-column feature grid is now a 3-story scroll. The countdown bar that looked subtle on a desktop is, on a phone, a third of the screen. Counting.
So you do the reasonable thing. You shrink it. Smaller font, smaller padding, smaller image, smaller idea, until the section that was supposed to grab people on a phone is a sad little rectangle that grabs nobody anywhere. The theme calls that responsive.
Some sections should not exist on phones. Not smaller. Gone. And some should only exist on phones, because a thumb wants different things than a mouse. A tap-to-call bar makes sense on a phone. On a desktop it's a button that calls nobody. A 6-image lookbook is a desktop idea. The phone customer wants the price, the button, the exit.
Some themes let you hide a section on mobile. Some themes. For some sections. App widgets, almost never. So you live with the sad rectangle, or you make the section twice and hide one copy with a line of CSS somebody on a forum swore works, and it works until the next theme update, because breaking that is the theme update's job.
Everyone who built the store looked at it on a laptop. The theme designer, the app developer, the agency, you. The only person who looks at it on a phone is the one holding the credit card.