Doing command-tab, then selected an app icon, then pressing down; this UX is a drill-down approach where you already know the window belongs to a particular app, and you drill-down from there.

I personally prefer the Windows approach where I'm shown all windows at once, in chronological fashion, and can use my performant human vision system to quickly identify the window I'm looking for. I believe that visual pattern matching beats other approaches such as thinking about which app is involved, typing first letters, etc.

To clarify, I think that if your flow if very static, then hotkeys for you apps (e.g. command+1 -> chrome, command+2 -> terminal) is pretty optimal. I would even buy one of those dedicated keypad like a supermarket/fast-food cashier would use. Direct access is best there.

But if your flow is more dymamic/organic; let's say you open a PDF, then work on something else, then want to focus on that PDF again; then I believe visual matching is best.

My opinion is not based on scientific studies though, it's just my own observation, so take it with a grain of salt.

Is this a way to switch between multiple windows of one app?