Thanks for your report, first I would try deleting the container, located in ~/Library/Containers/RawTherapee.
As per the crash report, it’s getting messed up here, probably encountering an out of bounds character
g_utf8_get_char + 0 which is possibly in the filename of an image in the startup directory. Could it possibly be reading some filenames with non-ascii/utf8 sequences in the path? It would be nice to be able to replicate the error.