Note that I don't want to open a specific app, I want to access a specific instance of that app. Think of an example when I have multiple Chrome windows open, and I want to open a specific one, since that has a group of tabs open. The principle is generic, I might want to open a specific IDE window, as I've got multiple instances open at the same type.
Absolutely every Mac user I've seen had to swipe through all their open app, or has to open the app and from the app then choose which instance they want to work with.
One of the hardest things about being a "power user" is watching other people use their computers in horrible and inefficient ways. There's a few different ways to get to a specific window on a Mac using the mouse. But I would add that using the mouse for this is probably less efficient than alt/command+tabbing anyway.
I think however this is achieved in mac by right clicking on the app icon in the task bar, then it has a list of open windows. In Windows, this is done by mousing over the app icon in the task bar.