Apple's Calendar and Reminders apps are so closely related, it's baffling that the company never tried to bridge the gap. On any given day, you might have your meetings and events scheduled in the Calendar app, while the actual tasks you need to get done for those events live in the Reminders app.
But after upgrading to iOS 18 and macOS Sequoia updates (which you can currently try out in Developer beta), you won't need to jump between two apps anymore—your reminders will automatically show up in the Calendar app.