Before you get started, check Unity’s Requirements and compatibility documentation for iOS to make sure you’re aware of any limitations for developing a Unity application for this platform.
Unity distributes dependencies as modules which means you use the Unity Hub to install them. The module you need is iOS Build Support. You can install it either when you install a new Unity Editor version, or add it to an existing Unity Editor install. To install modules:
To build iOS applications, Unity generates an Xcode project and then Xcode builds this project into the final application. This means that if you want to build an application locally, you must install Xcode. Xcode is only available for macOS, so if your development machine doesn’t run macOS, you can’t build an application locally. However, Unity Cloud Build can build applications for you which makes it possible for you to develop an iOS application on a non-macOS machine.