4k Home Videos on Apple TV 4k

I've taken videos on my iPhone XS in 4k - both 30 and 60 FPS. I use Final Curt Pro to edit and join the clips into one home video. I've tried exporting as "Master File," "Apple Devices," "4K" (using Compressor). The resultant QuickTime file (.mov or .m4v) shows the correct dimensions: 3840 x 2160. I share the iTunes library from the iMac (2016) to the Apple TV 4k. Other 1080p files play flawlessly, but when I choose a 4k video, a message appears on the Apple TV: "This content cannot be played because its format is not compatible with Apple TV."

No videos include both 30 and 60 FPS clips, nor do they include any clips shot in 1080p.

All HDMI cables are new High Speed Belkin cables sold at the Apple Store.

The TV is a new Samsung 4k TV. The Audio and Video Preferences from Apple TV show 4k UHD. The HDMI cable test passes.

I've reset and restored the Apple TV 4k. The issue persists.

Any thoughts? Thank you!