The behaviour of the Alt key is weird and varies in different applications. I did the following experiments.
Basic setup: Have some programs open so that they are displayed in the task bar
Go to an application, i.e. have it as the “active” one Press the Alt key Point with the mouse to another application in the task bar and click. The application becomes the active one. Release the Alt keyWhat I see is:
If the target app is Mozilla Firefox or Thunderbird or VLC, the menu is reliably activated upon releasing Alt. If the target app is MS Excel, menu is never activated. Excel activates the menu (displays shortcuts) a second after pressing Alt, i.e. not upon releasing it. If the target app is NP++ or LibreOffice the behaviour after releasing Alt is unpredictable. Sometimes the menu is activated, sometimes it’s not.As I wrote, I remedy the situation by changing the key to one without Alt.