The issue you are seeing is not a mistake in Slidev or a missing setting on your end. It is actually a well known limitation built into iOS. Slidev is a web based tool that relies on the Fullscreen API to take over the entire display. Apple deliberately disables this feature on iPhones to prevent websites from mimicking native apps or creating deceptive user interfaces.

Since this is a restriction at the system level, there is no way to force a true fullscreen mode through the browser. However, you can get very close by using the Add to Home Screen feature. If you open your presentation in Safari and add it to your home screen, it will launch without the typical browser address bar and navigation buttons. This provides a much cleaner experience that feels almost like a native application even though it is still running through the web.

If that does not suit your needs, you can also rotate your phone to landscape mode and scroll slightly to hide the remaining browser interface. For a completely distraction free presentation, your best options are to export the slides as a PDF or use a different device like an iPad. On those platforms, the Fullscreen API is fully supported and the Slidev interface will behave exactly as you expect it to.