Apple put a tremendous amount of effort to ensure that their apps and platform is secure.
In iOS 11 which launched in 2018, Apple allowed the ability to record the screen. You had to add a special screen record button to your control center and you could record the screen. If you long pressed the button then you could pick an app like See to send the recording to.
This process was a bit cumbersome so in iOS 12 Apple made it much easier by allowing the installed app to bring up the screen recording facility built into the OS. This feature is what See uses to record your iPhone screen and then broadcast it to your friends in real-time.
We take this stream and pass it to our global network of 100 servers to deliver the stream and transcode it so it is viewable on the web and Android versions of our app with a sub 1 second latency.