Hi Gun2Katana,
We understand you're not able to locate a 4K version of a movie. We would be happy to help. Please note from the following resource "Icons that appear on a movie's product page show the highest quality format that the Apple TV app offers." Also, "If you previously bought an HD movie from the Apple TV app, you might have access to the 4K, HDR, Dolby Vision, or Dolby Atmos enhancements on a compatible device. If your purchase doesn't have a high-quality version now, it might be added later.":
Find movies with 4K, HDR, Dolby Vision, or Dolby Atmos in the Apple TV app
Hope this helps!
Have a great day.