I actually figured it out. It turns out the HDMI 2.1 cable going from the TV to the capture card was connected the wrong way... I noticed it when I saw one end of the HDMI had “Display” on it, and the other end said “Source.” I’ve never seen that on a HDMI cable before.

It wasn’t an easy fix, because I had to run two 75 ft. HDMI 2.1 cables through my basement to get this going in the first place. I got lucky with the other HDMI cable going from my Xbox to the capture card, because I connected it correctly the first time. Having to undo all that work to pull up the entire HDMI cable through a small drilled hole on the 1st floor, only to run it through the basement again was a pain, but I got it done.