Hi, I have come across the same issue, icons on getting displayed, after upgrading Ubuntu 20.04 from Ubuntu 18.04.
The below-mentioned solution worked for me. It might work for others as well:
The issue might have occurred because the installation did not go according to the plans.
The simplest, easy and the most effective operation you can do is:
sudo apt dist-upgrade
This will automatically install/update/repair all the needed packages for your current version.
Hope this helps! 
Congratulations from me, it worked perfectly!
Your workaround worked for me:
`sudo sed -i '/Icon\[/d' /usr/share/applications/*.desktop`
`sudo sed -i '/Icon\[/d' /usr/share/mate/desktop-directories/*.directory`
`sudo update-desktop-database`Thanks, works for me
Hi!
I installed Ubuntu MATE 20.04 some days ago and this problem with menu icons is still around. The solution provided above has solved my problem.
By the way, I'm loving Ubuntu MATE 20.04! Coming from 16.04, I can see significant and great improvements in this new release.
See you!
Marcelo
This works for me
Thank you very much Azardo !!! 
