darktable is fantastic and getting better all the time.
In its feature development, it has gained many ways to narrow down a large library of images into a set of images to work on. This has caused the collect module’s source list to grow to be quite large and in an ad-hoc way. It’s not easy to find common things like “tag”, for example, and the list feels now very long and unorganized.
Hopefully this is easy to fix in darktable. I know the widget exists to group items, as it’s used in the overlay selector in the darkroom area, so it should be possible to use it in the lighttable area too.
I would switch lists between color labels and tags. I think the first is more basic for image selection during editing, while the second is actually exportable metadata.