sgentle parent
I use an iPad (that I have with me anyway) + cheap USB HDMI capture dongle for this.
What kind of dongles are compatible with iPad? Does it need some crappy proprietary app to view?
Pretty much anything – I just bought a random cheap one from Amazon, though you might get better latency for more money. The dongles show up as USB cameras (ie UVC) which is supported since iPadOS 17.
I use the (free) Orion app, but it's basically just a fullscreen camera preview so there are plenty of other options.