I have been using the RT dev appimage for the past few months on Ubuntu.
I downloaded the RT 5.9 appimage recently and installed it on the same laptop.
I realized that it is not picking up the few settings changes I made for RT-Dev appimage (mainly Favourites tab). I think these are stored in the options file under /home/xxxx/.var/app/com.rawtherapee.RawTherapee/config/RawTherapee
What is needed to make RT 5.9 use the same settings?
Yep, that is the out-of-the-box location RawTherapee looks for its local configuration files.
Just in case: If you want to run 2 (or more) versions independent of each other you can do so by setting RT_SETTINGS and RT_CACHE (and maybe TMPDIR if needed).
You can set it up for the AppImage version like this for example:
rta sets up the correct environment and starts the appimage in this example.
One of the reasons you might want to do it this way is that RawTherapee always writes its options file when shutting down. It will discard stuff that is part of one version and not part of the other and I’m sure that is unwanted in 99.9 percent of the cases.