The dependency of monitor adapters with mac models and macOS Versions - how does it work?

Hello,

since years I try to understand why - if I have one and the same monitor - but different generations of iMacs or MacBook Pros - I cannot find a suitable adapter by just following some simple steps.

Example: Let us say my monitor requires a dual link DVI connection. And I have one of the new Thunderbolt 3 ports at my iMac. Why can I not just google for a dual link DVI-(I/D) female connector to USB-C (where the advert says it is Thunderbolt 3 compatible)? Often I have to try 2-3 different brands to find one that works.

Is it that the adapter company needs to get specific protocols from Apple and is just not doing that when they develop their new adapter models?

What is Apple actually changing from iMac generation to iMac generation or macOS Version to macOS Version? Is there a place where I can find more information about these changes so that I can contact the adapter manufacturer with specific questions whether their model adheres to this new standard?

It is a riddle for me and I wonder whether I am missing a place where I can find that sort of information.

Does anyone know please or can point me somewhere?

I do not even know whether that is a mac hardware question or a macOS question :)?

Thank you!