hi
please your help to change mainmenu icon ubuntu mate 18.04
br
Right click on the mate-menu icon and then click preferences. A window will show up. There should be something called button icon there. By default mate-logo.svg is selected for menu icon.
You can click on that and a window will pop up in the /usr/share/mate-menu/icons directory. All mate-menu icons are saved here.
If you want to use a different icon, then you need to save that icon(normally a .svg file) on /usr/share/mate-menu/icons directory.