I’m having the same problem as several other who have posted here. In RawTherapee for MacOS Catalina, the file browser is unable to access any system folders and as such I cannot open RAW files from within the app. I can open them by double clicking in the finder however.
I’m using the latest version from the official website. I’ve seen others recommend using some of the builds at https://keybase.pub/kd6kxr/ and I tried downloading from there but when I try to open the .dmg file (any of them) I get the error message “RawTherapee…is damaged and can’t be opened. You should move it to the Trash.”