App link: https://apps.apple.com/de/app/ndi-hx-capture/id1501247823
Their NDI HX camera app is also currently free. It turns your iPhone / iPad into a low latency wireless webcam.
You can use these with the OBS NDI plugin or the software provided by Newtek which turns an NDI source into a virtual camera.
If you're just looking to share your iOS device to Zoom or other meeting apps, you can long-press the Control Center "Screen Recording" icon to select which app to direct your screen sharing to.
If you'd like your iOS/tvOS device to be shown in a window on your desktop using only native iOS/tvOS/macOS tools, you can plug it into a macOS computer and use Quicktime Player > File > New Movie Recording and then select the iOS/tvOS device from the dropdown to the right of the Record button — no need to start recording — and it'll give you a live low-latency view of the iOS device.
Is there anything this good an Android? There's a lot of apps that promise to do it but they look a bit suspicious and I'm wary about putting them on my phone.