Hi everybody
I’ve got a question. After last update I’ve seen already THREE update notification icons in my tray:
I wonder, are all of them REALLY necessary? Is it possible to integrate all of them in one?
Also sometimes they’re showing different updates…
I’m a bit lost 
Probably because you have 3 different programs to update?
The green one is octopi. I don’t recognize the icons of the other two, but my guess is that one of them will be manjaro-settings-manager-knotifier — which only notifies you of new kernels and may possibly warn you if you’re running an EOL kernel — and that the other one will be pamac-tray-icon-plasma.
Considering that the latter is essentially a substitute for the octopi notifier icon, you should disable one of them. pamac does handle FlatPak and Snap, while octopi does not, so if you have any Snaps and/or FlatPaks, then it is probably better to stick with pamac-tray-icon-plasma and disable octopi in the system tray settings.
1 is from Octopi
2 is from Pamac notifier
3 is from Discover
Which nobody should be using, because it uses the unsafe packagekit for elevating privileges. 
It can be safely used only for updating user installed widgets, themes/icons/cursors/styles…, sounds, wallpapers, splashes…
The packagekit problem is not KDE one, it’s a problem from Arch Linux and its based distros for not updating and fixing packagekit backend for their distros, other distros like Fedora, Ubuntu, openSUSE properly support packagekit without any issue.
No
No.
Discover is not designed system maintenance - Disable update check in System Settings → Software Update → Notification frequency → Never
The octopi application is really nice for Plasma
Pamac can be disabled in the Preferences for the application.