As of R3 2018, RadMenu exposes a boolean IsMainMenu property which indicates whether RadMenu receives a main menu activation notification. When set to True and the user presses the F10 or the Alt key, the menu grabs the focus and its first item gets highlighted. The default value is False.
Figure 1: RadMenu with IsMainMenu set to True once Alt/F10 is pressed
If there are multiple RadMenu instances with IsMainMenu set to True, only one of them will get highlighted.
If the mouse is captured at the moment when the activation takes place, the RadMenu will not receive the focus.