Is there a way to add an event to calendar with SwiftUI?

I think there is no build-in component for calendar in swiftUI but you try eny other third-party calendar controller for swiftUI like: https://iosexample.com/swiftui-simple-calendar-date-picker-for-ios/ or https://iosexample.com/tag/calendars/

What you're trying to accomplish is a data operation done using the Swift language. SwiftUI is a framework for creating user interfaces. Generally, you want to separate your business logic (backend code like storing and editing data) with your UI logic (which is a visual representation of your data).

For your question, you would want to create a separate class that can add/remove data from Calendar. While it's a bit too much code to discuss in a StackOverflow post, you can refer to a couple of documents to get started:

Apple's EventKit Documentation

This link shared by bartonstanley is also useful:

Add Event to Calendar iOS Tutorial

Once you have created a class that can manage calendar information, you should either instantiate it and create it in the view you need, or use the Singleton model. This way, you don't have a SwiftUI view with 100+ lines of EventKit-related code that doesn't involve the UI.

I hope this helps!