Yes, Rawtherapee, like Lightroom and other tools that use a non-destructive workflow basically just save the steps you take to edit something and save it separately. In my case, in the sidecar file. So my changes are there, but saved separate from the image.

Lightroom does the same thing, and I had it save my edits in a sidecar as well, but because every editor is a little different, the results will not be the same if I were to try and have RT reproduce the steps that LR used (if they are even available). Basically, if I want to revisit my old photos processed in LR, I have to develop them again.

The sidecar files are just XML. You can open them in a text editor and poke around to see what it looks like.

I don’t really shoot much video, so I can’t speak to that. With digikam I mostly just use it to find photos and videos by date and/or metadata. digikam creates fingerprints for assets that it uses to locate things. I think I tweaked some settings to make digikam only compare the file hash instead of trying to match things visually. I’d rather have two copies of something than not importing a separate image.

I have used kdenlive for some basic video editing, but there are many options. You can even use Blender for video editing.