Can same application be opened in 2 different desktops in MAC
Desktops in MacOS are not like running a different machine. So yes, you are right, you can think of them as multiple screens.

That said, you can have the same application on multiple screens. This requires the application to be able to have multiple parent windows. E.g. this works fine with a browser: Open a second window on desktop 1, enter mission control, and drag the second window to desktop 2. Now you can change desktops and have the same program running on both with different content. Clicking the dock icon will cycle through all open windows of the app, also if they are on different desktops.

This does not work for applications that can have only one parent window, like most email programs or professional editing tools.