Hi.
In Ubuntu MATE 18.04 -- how can I remove just the power option icon (image attached) only from notification area? If I remove it -- the whole notification area gets removed. I don't recall this behavior in previous versions of MATE/Ubuntu MATE.
Thanks.
Run this command to remove the indicator
sudo apt remove indicator-session
then log out and log back in and it should be gone.
(This will remove it for all user accounts. I don’t know how to remove it for just one user.)
And just to be clear, this is the indicator shown in your image, with things like “About This Computer”, settings, Log Out,and Shut Down, not the power indicator (indicator-power) that shows battery status for computers with batteries.
Thank you elcste. That solved it! 
If you are still interested in removing only the power icon, you might try going to /usr/lib/x86_64-linux-gnu/indicator-messages/ and rename indicator-messages-service adding dot disabled. Log out and back in and only the power icon is removed. This avoids removing all the systray icons.
Hi mdooley.
As elcste said, I was wrong in calling it the power indicator - it’s the ‘indicator-session’. Or do you also refer to the thing I highlighted in the image?
Thanks anyway.
For some odd reason - I’m not receiving any email notifications for replies to this thread. 
I looked a bit closer at your screenshot and saw that the icon you had circled is not the power icon and is as elcste described it. If you are happy with removing the entire indicator-session (which will also remove your ability to use Mate Tweak to change your panel layouts) then great. Good luck @Rarmorog.
Hi mdooley. I did not know it would affect MATE Tweak. How would I only remove the icon in question without affecting MT?
As far as I know, you can’t. It’s either all or none. If you want Mate Tweak to be able to change your layouts, you should reinstall the indicator-session. See this post - UM 18.04 mate tweak not working as it should for how I know this.
With this indicator removed you can still use MATE Tweak to save layouts and switch to layouts you have saved. I have been using my main home computer with this indicator removed for months now, which I actually had forgotten about until this post came up 
and I have changed my layout and saved it. I just tried it again now and it worked.
What does happen, though, is that many (nearly all?) of the predefined layouts (like Mutiny and Cupertino) no longer show up in the MATE Tweak list for you to choose from. (I only see my own saved layouts and “GNOME2”, but I’ve also removed other things like Plank that are needed by some layouts.)
@Rarmorog I don’t know how to remove this indicator and keep the layouts showing up, but you can always reinstall it if you want to change layouts and then uninstall it again.
If you really wanted to try, it looks like the “meat” of the indicator package is are the binary itself
/usr/lib/x86_64-linux-gnu/indicator-session/indicator-session-service
and the systemd service
/usr/lib/systemd/user/indicator-session.service
You could try keeping the package installed but delete the binary or edit the systemd service file so it doesn’t start. You may get errors since the package would be essentially (intentionally) broken. [Edited after reading closer the post that @mdooley linked to.]
Linux Mint 19 does not have the icon.
I wish there was at least an option to hide it in UM 18.04.