On my way to testing out 24.04 I ran the upgrade from 22.04 to 23.10. Now when I log in I get a desktop with an icon for my home directory, but there is no menu bar. My system was configured to use Compiz as the window manager; I presume that would have been preserved. I found an article suggesting that Compiz can cause an empty desktop and missing menu bar and that switching to slick-greeter might fix the problem. I've tried that without success; except for the greeter, nothing changed. I can use the standard keyboard shortcut to start a terminal, but without the menu bar the system is almost unusable. Until I find a fix for this, there doesn't seem to be much point to taking the next step and upgrading to 24.04. Any suggestions? (This is all happening on my laptop, which is not my primary computer - I'm still on 22.04 on my main system and plan to stay there until 24.04 is running smoothly on the laptop.)
Welcome @dgtangman to the community!
Open a terminal and issue this command:
mate-tweak
you can reset your layout and/or switch from compiz to marco here.
Been there, done that, thanks. Unfortunately, marco doesn't provide the one accessibility feature of compiz that I use all the time - enhanced zoom.
You don't have to switch to marco, but you might want to reset your layout so that your mate-panel (or "menu bar" as you call it) can be re-placed.
Anyway, since you hinted that you've already did reset your layout, the next step would be this:
Would you be so kind to issue this command in a terminal and report the output back ?
mate-panel
"Cannot register the panel shell: there is already one running."
Possibly useful information: If I log in with marco set as the window manager, mate-panel displays as expected. If I switch to compiz, mate-panel continues to operate as expected until I log out. Logging in with compiz as the window manager leaves me with no mate-panel display, but mate-panel is running.
On a whim, I tried killing the mate-panel process in a compiz session. That got me a new mate-panel process that displayed and operated normally. Except that remapping the Window key to Super doesn't seem to work, which makes my Enhanced Zoom under compiz not work.
It certainly is ! 
It would be a good idea if you filed a bug here:
https://bugs.launchpad.net/ubuntu-mate
Probably because what is called a "race condition".
The start of the panel should be delayed until compiz is up and running.
As a workaround you can automate the restart of the mate-panel, you can create a new item in "startup applications" and use the command "mate-panel --replace", also set the delay at 3 seconds or something like that. This makes sure compiz is ready before the panel starts.
Also check in CCSM if mate-compatibility is enabled , you might want to do a "reset CCSM" first.
AFAIK the Window key is the Super key but the keybindings in compiz differ a lot from the keybindings in marco. You might want to customize that in CCSM also check if there are no conflicts between the keybindings.
A race condition it is. Bug report filed. I tried the mate-panel restart with a two-second delay, and that has worked consistently (in three or four trials).
It turns out that my Window/Super key mapping problem wasn't real. I was trying to test it with xev, but apparently the Super keypress is intercepted before it can get to the xev window. The problem with Enhanced Zoom not working is that I had at some point turned on the software compositor, perhaps accidentally, and that was preventing Compiz from initializing completely. With that corrected, everything is now working as expected.
Same problem going from 22.04 to 24.04 fixed same way thanks!!!
Now trying to find why the dock and other configurations are missing, but this was a real blocker.
Hi, @Agustin_Bosso and welcome to the Ubuntu MATE Community!