Well, most probably it will be a matter of the dbus version: Linux Mint 19.3 is based on Ubuntu 18.04, and perhaps 2 years is a bit too much for certain package dependencies.
And as Linux Mint 20 seems to be around the corner, it’s just a matter of waiting a bit and see what happens…
Well I’ll open from Windows Experorer more often than not. Or I’ll sometimes open a selected raw (nef) file from another program. I suspect that always using RT’s internal browser is the workflow of the 'leet “expert” users, while us duffers will often open files from Windows Explorer or some other program instead.
As to why I want to open from Explorer, it’s because I’ve already identified the file I want to edit in Explorer (or whatever other program) and don’t want to waste time hunting it up again in the RT thumbnail browser.