4K movies from library not showing on apple tv
I just got an Apple TV 4K, and a large screen LG smart TV. I have a 4K capable HDMI cable from Belkin (recommended by Apple for the ATV4K). None of my 4K movies in my TV library on my iMac are showing up on the ATV. It's frustrating, because it would be nice to watch these movies on the 55" TV instead of my 27" iMac. Isn't that the whole point of the ATV4K?
I could set up Plex and watch them through that, but I shouldn't have to. That would require copying the 4K movies to a separate folder for that purpose.
Is there a setting I need to change? I've rebooted the Apple TV, I've unplugged it and waited ten minutes before plugging it back it, all to no avail.
My TV is the LG 55" Class C1 Series OLED 4K UHD.
Apple TV 4K, tvOS 15