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.
I use the (free) Orion app, but it's basically just a fullscreen camera preview so there are plenty of other options.