Hi CasinoKiD,
Thank you for using the Apple Support Communities. I understand you have a question about a 4K version of an iTunes Store purchase.
When you say you don't have the option to purchase the 4K version, what exactly are you seeing? Do you receive an error message? If you do, what does it say?
What device and software version are you using?
Are you currently using a 4K-compatible device? The information below is from the resource titled Find and watch movies with 4K, HDR, Dolby Vision, or Dolby Atmos:
"Find your device in the table below to see if it can play 4K, HDR, Dolby Vision, or Dolby Atmos content.
Device
Media
iPhone 8
iPhone 8 Plus
iPhone X
iPhone XR
iPhone XS
iPhone XS Max
iPad Pro (10.5-inch)
iPad Pro 12.9-inch (2nd generation)
iPad Pro (11-inch)
iPad Pro 12.9-inch (3rd generation)
Can play HDR and Dolby Vision content.
iPad Pro (11-inch) and iPad Pro 12.9-inch (3rd generation) can play 4K, HDR,
or Dolby Vision content to a compatible connected display or television.
Apple TV 4K
Can play 4K, HDR, and Dolby Vision content to a compatible connected television.
Learn more about playing 4K, HDR, and Dolby Vision content with your Apple TV."
I hope this helps get you started. Kind regards.