Yes, it’s one window and the “focus bar” says “Focusing on Project A” even when I’m in Perspective B, and then I see actions (and project names) for all projects.
Before I posted I tried in v86.0.206686 and one previous version. I just updated to v86.0.206687 and it behaves the same. I’ve double checked, as I messed up before in this thread where my original description was incorrect … ;-) That time I used my normal projects and hierarchies, and it was harder to see exactly what was happening. Now I’ve made exactly the same arrangement as described above (though in my normal library) and get the same result in all three versions I’ve tested.