If you really care about fidelity you’d skip the streaming and either have a collection of new and used blurays, rip blu rays from the library, or pirate bluray rips from other people.
No one offers actual fidelity on the streaming platforms. They consider cost to them to serve content and assume you don’t care enough to seek alternatives.
Some movies like Avangers End Game are presented in 16X9 Dolby Vision on Disney+ vs 1X2.35 HDR10 on UHD Blu-ray. You can look up comparisons on Youtube if you want to.
So it is not always the case that the UHD disk is better in all aspects.
No one offers actual fidelity on the streaming platforms. They consider cost to them to serve content and assume you don’t care enough to seek alternatives.