In resolution 4k is not an option

with a 4K capable HDMI cable

Indeed, the cable can be a reason for lesser resolution from your HDMI devices. Verify the HDMI cable to be rated for 18 Gbps (aka ‘Premium High Speed’, aka ‘HDMI 2.0 compliant’).

Not all content is streamed via 4K, for example if you subscribe to Netflix they have a 4K package. However, if you subscribe to Apple TV + I believe all the current content is in 4K. In order to get 4K you need the following:

• Apple TV 4K
• 4K content on the Apple TV 4K device.
• 4K TV (connected to the Apple TV with a 4K capable HDMI cable)

Hello,

Do you have your Apple TV 4K connected to a 4K TV?