how to deliver UX and UI for different desktop screen sizes?

I have recently started doing freelance work and for my design I started using AdobeXD. The client has asked me design a single page website containing some 3-4 static sections, hero section included along with dedicated section for footer.

I have completed my wireframe and finished the UI and deliver every static assets to the dev team.

Now I told the dev team the UI was designed for 1920x1280 screen but most of the developers are using 1336 or 1280 screen size and they were keep asking design for these specific screen sizes.

I am confused here -

  1. Do I have to design all the UI screens for two different device screen sizes? If yes, wouldn't that make the work redundant which, to me, doesn't make sense at all.
  2. Can dev team just make them responsive for the other two screens based on the given UI?
  3. What if the website has to made responsive and adaptive for higher resolutions such as 2k and 4k?
  4. If none of the above is true, what is an actual way to deliver a project for different desktop screen sizes? What is the design method/process those large design studio follows to delivers project to responsive and adaptive to different and larger screens?