Keyboard shortcut for the “Start” whisker menu is, by default, Alt+F1 (xfce4-keyboard-settins > application shortcuts)
However, the ‘Super’ aka ‘Start’ button still brings up the whisker menu.
I changed the shortcut from Alt+F1 to Ctrl+Escape, and put Alt+F1 as xfdesktop --menu.
Now, suddenly, the Super key pulls up xfdesktop menu.
After some research, I found that the culprit is xcape, specifically, in xfce4-session (Session and Startup) > Ajpplication Autostart, we find xcape and when you hit edit, we have xcape -e 'Super_L=Alt|F1' set to trigger on login. To verify this on a system just run ps -ef | grep "xcape"
Fix: get rid of xcape entry and put in a default Keyboard shortcut in xfce4-settings - Keyboard > Application shortcuts
Having a daemon run at startup to redirect a keypress seems helpful, but is a bit hard to figure out if the behavior is not as expected / wanted.
A beginner just starting to customize their desktop could get confused at this behavior as it is not clear that there are keyboard behaviors defined in non-obvious ways using 3rd party utilities – speaking of which, the Window manager keyboard shortcuts should probably be linked to from keyboard shortcuts as well, as it’s not obvious that there’s at least two separate areas to manage keybinds.
Resource immensely helpful in pinning this down quickly for me:
unix dot stackexchange dot com slash a slash 596140