How long does it take for RPD to complete 'probing' ?

I finally got RPD to ‘see’ my camera; it says it is ‘probing the device’. It’s been doing that for nearly an hour - do you think it has found anything yet?

This suggests gphoto2 is having trouble communicating with the camera (it happens on rare occasions). Remove the camera and try again. Of course, I am assuming your camera is supported by gphoto2. Have you confirmed it is? This is the list: http://www.gphoto.org/proj/libgphoto2/support.php

Yes, the camera is on the list of those cameras support by gphoto2 as of October 2020. Getting to the point of the camera being listed as a device in RPD took about 2 hours of repeated ejecting of the USB device listing in Nemo, unplugging the camera, turning it on and off, rebooting Linux Mint 20 plus other actions that I have now forgotten. I managed to get the camera listed only once and have no idea what the magic incantation was that successfully achieved this. Today the camera is not detected by RPD, but the SD card is - however, without contents until I invoke Nemo and click on the icon for the Card, listed under ‘Devices’.

If you are saying that your camera was supported by gphoto2 starting October 2020, then Linux Mint 20 will not support your camera without manually upgrading gphoto2.

If you are saying that you consulted a list of cameras that was last updated October 2020, then depending on the camera, gphoto2 on Linux Mint 20 may or may not support the camera. It depends how new your camera is.

What is the camera model you have?

Sorry, missed this question (for some reason). Camera is Fujifilm X-T30

It might be useful to know, in case you didn’t already, that Rapid Photo Downloader (or any other program) simply cannot access the camera when it is mounted by another program, like Nemo or anything else that uses Gnome’s GIO.

That is an unfortunate reality. Only one program at a time can access the camera. Gnome’s GIO automatically mounts the camera whenever you plug it in, taking control of the camera. (Mint, like most other Linux desktops, uses GIO; KDE does not).

Rapid Photo Downloader requests GIO unmounts the camera so it can access it itself. Normally this happens automatically, without error. However occasionally things can go wrong.

I don’t recall exactly which version of Linux Mint you have. Is it version 20? From the gPhoto2 news file, it says your camera has been supported by libgphoto2 since version 2.5.23.

Anyway, does it work now?

Sadly, no. I do have libgphoto2 version 2.5.23-1 install led in my Mint 20.1 Cinnamon 64 bit.

One factor to consider is that I still cannot be sure if this is a user error or not: for example is there a special order in which ‘things’ have to be done, like the sequence of such tasks as connecting micro-USB cable to camera, connecting USB connector to PC, power-on the camera, start RPD, mount the camera in Nemo or dismount the camera.

What I do notice is that when the camera and PC are connected no device is (apparently) detected by Mint until the camera is powered on - even though the camera is showing an illuminated LED as soon as the cable is connected to the camera. Even after powering on the camera, the ‘device’ is not mounted. Actually two devices are listed in Nemo, both as ‘USB PTP Camera’, with identical defining character strings, aside from the last in a string of about 20 characters.

RPD lists the camera under ‘DEVICES’ whether or not it is Mounted in Nemo, but it remains in a ‘probing device’ state indefinitely irrespective of the mount status…