DIAGNOSIS This points to a problem with that specific HDMI port on the TV. It could be a software glitch with its EDID detection, a physical connection issue, or (less likely) a hardware failure of the port itself.
FIX First, force a fresh handshake. With the TV on and set to the problematic HDMI input, unplug the HDMI cable from the TV, wait 10 seconds, and plug it back in firmly. Then, power cycle the device connected to it (console, streamer, etc.). If that fails, try a different HDMI cable on that specific port to rule out a cable/port combo issue.
IF THAT DIDN'T WORK Go to Settings > System > Power > Restart (not just power off). This performs a soft reboot that can clear port detection errors. You can also try disabling 'HDMI Auto Game Mode' or 'HDMI 2.1 Mode' for that specific port in the TV's input settings, as sometimes the enhanced mode can cause compatibility problems.
HEADS UP HDMI ports can get damaged from frequent plugging/unplugging. If only one port is dead and a restart doesn't help, you might be stuck using the other ports. It's a repair if under warranty.