I am having the same issue. I have changed the capture card's resolution in the nvidia control panel from 4k to 1080p for the PC i am trying to project to. No matter what, the resolution is coming up as 720p for the full screen projector. Anyone have a fix for this?
Clarification: the capture card is on the other PC but i changed the resolution for it on the PC i am trying to send the full screen preview too.