Jasem and Jantje:
I have a Nikon D750 and I can assure you absolutely everything works fine. I've put in attachment some screen copies with my settings, if this helps.
On one screen, you can see a red dot facing the definition, this is normal. The screen copy was taken after I used the live stream, so the definition is that of the rear screen.
When you take still images, the definition returns to 6016x4016 and the red dot goes green again.
Jantje, for your third problem (the connection) look for a file /usr/lib/udev/rules.d/99-nikon.rules. it should contain ...
<
ACTION=="add", ATTR{idVendor}=="04b0", RUN+="/bin/sh -c '/bin/echo 256 >/sys/module/usbcore/parameters/usbfs_memory_mb'"
SUBSYSTEMS=="usb", ATTR{idVendor}=="04b0", MODE="0666"
>
... so every one can read and write the device.
The same directory should also contain a 85-disable-dslr-automount.rules with ...
<
# Disable automount by setting envrionment variable for UDISK2.
# Pentax
SUBSYSTEMS=="usb", ATTRS{idVendor}=="25fb", ENV{UDISKS_AUTO}="0"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0a17", ENV{UDISKS_AUTO}="0"
# Canon
SUBSYSTEMS=="usb", ATTRS{idVendor}=="04a9", ENV{UDISKS_AUTO}="0"
# Nikon
SUBSYSTEMS=="usb", ATTRS{idVendor}=="04b0", ENV{UDISKS_AUTO}="0"
# Sony
SUBSYSTEMS=="usb", ATTRS{idVendor}=="054c", ENV{UDISKS_AUTO}="0"
>
... so the device won't be set "busy" when the driver tries to access it.
Jasem, I also have a D3100; it works fine except for the live video, which is not supposed to. The D3100 in a low end Nikon, so it isn't as feature-rich as the high end cameras like the D500 or the D750. Being from the same bloodline, I wouldn't be surprised should your D3500 have the same problem. But I repeat, everything else works fine.
In the live video, it you click the debayer, everything goes boom.
Well, I hope all this helps
- Marc