It seems it's not well-known how to undo a Minimize All or a Show Desktop, two operations which I discussed briefly yesterday.
To undo a Minimize All, you can right-click the taskbar and select "Undo Minimize All", or at least you used to be able to do that. Minimize All is no longer on the menus, presumably because it ended up redundant with Show Desktop.
So after you do your ÿ+M to Minimize All, you can type ÿ+Shift+M to Undo Minimize All.
To undo a Show Desktop, just click Show Desktop again. If you used the keyboard accelerator ÿ+D, just press it a second time.