|VK_RMENU 0xA5. Usually mapped to a pop-up menu that can alternately be accessed by a right mouse button click if the app is programmed for it.|
Exactly that one, the one to the left of the right Ctrl key in here: https://en.wikipedia.org/wiki/Keyboard_layout#/media/File:Physical_keyboard_layouts_comparison_ANSI_ISO_KS_ABNT_JIS.png
It is marked "Menu" but VK_MENU is the Alt key. VK_RMENU/0xA5 you said? I'll try it.
BTW, in this layouts the Return key is marked "Return", the photo linkted in the OP markes it "Enter", also the one in the numeric keypad. So it's hard to explain someone the difference between Enter and Return.
: following extension:
I tried it with ooDialog
(an supplement of ooREXX), but with a pop-up menu defined together with the right mouse button also this "Menu" key is activated by some user-friendly automatism I guess. So I installed Carnac https://github.com/Code52/carnac/releases/tag/2.2.155
-- which tells me, this "Menu" key to be Apps
VK_APPS/0x5D, Applications key.
Found it (p. 1381 of 1872):
|The event handler for the context menu event is invoked when the user right-mouse clicks on a window, types SHIFT-F10 on the keyboard, or types the VK_APPS key on the keyboard. The VK_APPS key is the Applications key on a Natural keyboard.|