Exercise 1: One Underlying Choice, Two Symptoms — Possible Solution
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THE UNDERLYING CHOICE
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Per this chapter's own finding-box, the single underlying choice is that macOS manages interface state primarily PER APPLICATION, while Windows 11 manages it primarily PER WINDOW.

HOW THE MENU BAR BEHAVIOR FOLLOWS FROM IT
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Because macOS treats the application - not any one of its windows - as the primary unit, there only needs to be one Menu Bar for the whole screen, and it simply displays whichever application is currently active. The menu bar isn't owned by a window at all; it's owned by the app, which is exactly why it keeps showing that app's menus even when one of its windows is hidden behind another app's window.

HOW THE DOCK/QUIT BEHAVIOR FOLLOWS FROM IT
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For the same reason, closing a window doesn't end the application's lifetime, because the window and the running application are two different things in this model. The application keeps running (and keeps its Dock dot) until it is explicitly told to quit, regardless of how many of its windows remain open - zero windows open doesn't imply zero processes running.

WHY THIS WORKS AS AN ANSWER
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It correctly names the per-application vs. per-window distinction as the single underlying design choice, and explains both the Menu Bar behavior and the Dock/quit behavior as direct, separate consequences of that one same choice rather than two unrelated quirks.