I just found out (with Darktable 3.5+) that you can define a folder display under collection filter panel and it sticks between restart. (as far I remember keeping this filter setting (folder, filmroll…) wasn’t the case with DT 3.4, but I’m not 100% sure).
Darktable is not a photo oriented file browser, as digikam is. But is a library oriented software, which needs to be manually feeded by photos you want to keep and work on, as Lightroom or Luminar are.
With Digikam, you think of file first, that you want to manage and edit eventually.
With Darktable, you think of photo first, not file. You don’t care were the files are, you import in the library only what you want and work on the photos, not the files. File management is not meant to be part of Darktable.
In fact, Darktable manages only one huge library of all photos you import. Then, you can “group” these photos under different categories. One category is the folder they are in. This folder happen to be called filmroll in Darktable. But that’s only one way to see that.
I like better the folder view (in collection filtre panel), because I have multiple folders with the same name. The filmroll view confuses me a lot.
I also wish these folders stay open and I could resize the panel to a taller size too ^^ But that’s another topic