New
#11
Could it be that the OP has a computer or laptop with say, a 32GB emmc disk? That could be why he hasn't updated in so long.
It's not the general "action center" notifications icon. It's a Windows Update icon as identified by Brink.
That Windows Update system tray icon was new in version 1803 (and since Build 17063 for Windows Insiders).
It can be removed from the taskbar by switching it off at Taskbar settings, Select which icons appear on the taskbar.