Hi1
I noticed an issue on ubuntu-mate with some snap packages not showing the icon in the appindicator.
It is fixed if I append "Unity" to the env variable XDG_CURRENT_DESKTOP.
But then the programs that have ShowOnlyIn=MATE (like caja) do not show in the menu.
Is there a different way to fix this?
Thanks
Welcome back to Ubuntu MATE community!
Which packages exactly? Which version of Ubuntu MATE?
One example of snap package is Whatsie, but also other ones (I'll test it with the env variable reset to the original value).
The versions of ubuntu-mate on which this happens are 20.10 and 21.04, I haven't tested older ones.
This really depends on the contents of Snap and its developer's skills.
The following snaps show their icons on latest Ubuntu MATE 21.04 normally:
1password - 
discord - 
slack - 
signal-desktop - 
skype - 
zoom-client - 
But there is wrong icon 
for shutter, whatsie and maybe others.
Some further technical analysis is needed.
I don't use Snaps, but can't you just make your own icon? I do it for other programs that don't have icons in the theme set. This is from a previous post:
The problem is not that the icon is missing, but that the appindicator does not show it (unless I append Unity to the env variable XDG_CURRENT_DESKTOP)