I can't use the add menu, how can I fix it? I'm starting now to modelling in blender, I was trying to create an hexagon, as everyone do, I searched on YouTube and here I understood that you need to do 3 simple steps:

Add a cylinder
Click on the menu in the left bottom part of the screen
Reduce the number of vertices

And the magic is done, but for some reason my add menu doesn't work properly, as you can see in the photo it seems impossible to change the properties and the first time i click on it, it disapears!
As moonboots told me the problem is that the Global Undo was disabled, to fix the problem you need to go here: Edit-&gt;Preferences-&gt;System and add the check on the Global undo