Yes. In darktable you can switch the crop aspect ratio between landscape and portrait without rotating the image itself.

In the older Crop and Rotate module, there is a button next to the aspect-ratio selector that flips a rectangular aspect ratio between portrait and landscape. The newer Crop module provides similar functionality. In darktable 3.8 and later, Crop and Rotate was deprecated and replaced by separate Crop and Rotate modules.

One important limitation: keeping the same aspect ratio but swapping orientation means the resulting crop will be much smaller than the original image. For example, a 3000×2000 portrait/landscape ratio flipped to the opposite orientation can only keep the dimension of the shorter side, so you lose a large portion of the frame. If needed, you could also mimic this by rotating the image, cropping to the original ratio, then rotating back conceptually — but darktable should let you flip the crop orientation directly.