There is no way to escape "&".

Here is my hack to show the key (it only works when & is the ending key):

diff --git a/src/Plugins/Qt/qt_utilities.cpp b/src/Plugins/Qt/qt_utilities.cpp
index 706c1d7..d25a502 100644
--- a/src/Plugins/Qt/qt_utilities.cpp
+++ b/src/Plugins/Qt/qt_utilities.cpp
@@ -203,6 +203,10 @@ to_qkeysequence (string ks) {
              << qks.toString (QKeySequence::NativeText).toLatin1().data() << LF;
     return qks;
   }
+  if (ends (r, "&")) {
+    // HACK: because Qt menu can not show the key &
+    r= r(0, N(r)-1) * "Shift+7";
+  }
   return QKeySequence (to_qstring (r));
 }

comment #2:

> comment #1:
> > Yes, this an annoying known problem, due to Qt.
> > It seems that there is no way to escape the ampersand.
> >
>
> It seems that there is a way to avoid this. You just need to use && to escape the ampersand in the menu.
>
> https://stackoverflow.com/questions/46580519/how-to-insert-a-special-character-into-qmenu-as-a-part-of-title-text/46580776
>
> https://doc.qt.io/qt-5/qmenubar.html#details
> "The ampersand in the menu item's text sets Alt+F as a shortcut for this menu. (You can use "&&" to get a real ampersand in the menu bar.)"

Yes, this an annoying known problem, due to Qt.
It seems that there is no way to escape the ampersand.