I have used this Elgato Camlink 4k USB for a live tracked camera (GoPro or Sony A7R) at 1080p60, it is supposed to handle 4k also but I haven’t tried that. The green-screen through composure works for me also. I can’t speak to Virtual Production stuff I haven’t tried. Some early examples of what I’ve tried are here https://www.youtube.com/user/GregCorson
I’ve also noticed quality of the video I’m getting doesn’t seem as high as I expected. I’m not really sure why, it could be the way I have things setup, cameras, lighting…etc. I haven’t had time to do a more careful test of my setup.
The main issue with something like the Elgato is that it doesn’t support genlock or timecode sync which makes syncing up live video with live motion capture more difficult.
Blackmagic products MAY work, but as I said earlier their Intensity Pro 4k did not work with some of my cameras and they told me there was no fix for this. They couldn’t say if the DeckLink cards or ATEM switchers would have the same issue or not, which is why I’m considering Aja.
For your purposes I’d suggest you make sure whatever you buy is returnable, just in case. If you have more recent vintage cameras you may have better luck than me with BlackMagic.
Also whether BlackMagic or Aja, if the card isn’t on the plugin’s “supported” list don’t expect it to work.