You are right, for some reason there are 2 versions of the movie listed on Amazon. One is HD for $9.99 and the other is $4.99 for UHD. The UHD one is hidden for me.

This was the one that came up with search, but I don't have prime. That could be it.

https://www.amazon.com/West-Side-Story-Ansel-Elgort/dp/B09HZCWP19/ref=sr_1_2?crid=52U27VVJT1K1&keywords=west+side+story&qid=1649259558&sprefix=west+side+story%2Caps%2C84&sr=8-2