On devices like the Zũmo XT the .System folder is invisible by default. This folder can be made visible by following these steps:
Go to View Map:
Click on the speed indicator on the map screen in the bottom left corner, to open this screen:
Long press the circular speedo, at least 5 seconds. The following screen will appear:
Choose "Configuration and Settings", next
"MTP Settings" and next
check "Show .System".
For users of a Mac there's one more challenge. The device is not visible in Finder...
You can solve this problem by using Android File Transfer. That program is able to access MTP devices. An optimal use of Android File Transfer requires a few more tweaks to be applied to it. Read this page to learn more.