Grabber (like Cam Link Pro) is passive device, your source must correct introduce list of resolution.

Ask your Support Technician about additional options available through our exclusive Priority Care Program. Windows Camera app, and Elgato Capture Utility both capture a perfect 3840x2160p 30hz video from that source.

I understand you want to use only part of your captured image, so your choice of the smaller canvas. This feels a bit like being told to unplug and re-plug my cable modem after stating that I have already done so, 14 times.

Then when I rescale it all back down to 1080p, I am right back where I am now, with my 4k source scaled to take up the entire base resolution.

And going back to beginning if you see in OBS (logs) this resolution 1920x1080 and FPS 60 - your source send 1920x1080p60. Perfect for live streaming, video conferencing, online teaching and more, Cam Link Pro makes advanced multicam production a breeze. The rest is like Tomasz told: crop and resize to fullscreen the 1080p upper left part of the Ultra-HD source as you wished.