In the Add to Panel
dialog this menu is listed as Classic Menu
. Just started happening with latest update/upgrade.
The 'Applications' item drops down as empty. A narrow gray strip. The position on the panel makes no difference.
Here is a complete list of apt list --installed | grep menu | grep mate
gir1.2-matemenu-2.0/focal,now 1.24.0-1 amd64 [installed,automatic]
libmate-menu2/focal,now 1.24.0-1 amd64 [installed,automatic]
mate-applet-appmenu/focal,now 0.7.3+dfsg1-2 amd64 [installed]
mate-applet-brisk-menu/focal,now 0.6.0-1ubuntu1 amd64 [installed]
mate-menu/focal,focal,now 20.04.3-0ubuntu1 all [installed]
mate-menus/focal,focal,now 1.24.0-1 all [installed]
mate-window-menu-applet/focal,now 20.04.0-1 amd64 [installed]