You may see an error like this from Nemo file explorer when attempting to browse into the NIKON DSC Z 6/store_deadbeef/DCIM directory:
The folder contents could not be displayed. Sorry, could not display all the contents of "DCIM": Failed to get folder list: -1: Unspecified error
If you're using darktable, you may see this error:
camera `Nikon Z6' on port `usb:something,something' needs to be remounted
make sure it allows access and is not mounted otherwise
In both cases, you will not be able to see any images on the camera.
If you install gphoto2 and run
gphoto2 --auto-detect -l you may see this error:
Nikon Z6 usb:something,something
There is 1 folder in folder '/'.
There is 1 folder in folder '/store_deadbeef'.
*** Error ***
PTP Invalid Storage ID
*** Error (-1: 'Unspecified error') ***
All of the above means that the camera is switched off. You just need to switch it on to be able to access the photos.
Hope this helps somebody!