How to reproduce:
1. Open the attached project "MainToolbarPinRepro"
2. Go to Repro -> "Bug 1 - Set up the stale pin, then register the menu item"
3. Open the Main Toolbar overflow menu (the ⋮ icon at the top right) -> Menu Items and select the "PinQA Dynamic/Runtime Action"
4. Observe the results
Expected results: The "Runtime Action" button appears in the Main Toolbar
Actual results: Nothing happens - no button is added and nothing is logged; because no button exists there is no right-click -> "Hide" entry to clear the stale pin either, so the only way out is Presets -> "Reset to Unity Default", which also discards the rest of the Main Toolbar layout
Reproducible with: 6000.7.0a4, 6000.7.0b1
Not reproducible with: 6000.6.1f1, 6000.7.0a3 (No such feature)
Reproducible on: macOS Tahoe 26 (M1)
Not reproducible on: No other environment tested