TL;DR: Clean up any mobile phone drivers you have and install Samsung's ones.
I wanted to update to the beta UI package. One method is via ADB sideloading, which I prefer compared to SD Card mounting. I started with:
./adb reboot recovery
on my system and everything was nice: I hot my phone in recovery mode. I immediately selected the option to "apply update from ADB". The phone started with:
Now send the package you want to apply to the device with "adb sideload <filename>"
Now, I started ADB (most recent version too!) on my PC with:
./adb devices -l
an I had the unpleasant surprise to see an empty list:
./adb devices -l List of devices attached
... and my phone soon timed out:
Timed out waiting for package Installation aborted #1
After some digging, I found out that you need to install the Samsung drives for Samsung phones, so I went and installed Smart switch from here.
Listing then yielded something like:
./adb devices -l List of devices attached 1234123412341234 sideload product:starltexx model:SM_G960F device:starlte transport_id:1