You could also try a different crop, losing a lot of the sky at the top and going for something more of a letter-box, with the horizon about two thirds of the way up the picture, without quite clipping the top of the mast to the left. I'd like to see what happens if you can get the boats in the centre to draw my eye a bit more - the little bit of river helps, because it leads my eye round in a loop finishing at the boats, but then I'm distracted by the bright sky beyond. If gloomy is what you want, see what happens if the sky does darker and more contrasty (but not too much!). One of my tests when trying to work out what I want to do with an image is to ask myself 'do I believe in the light in this picture?' With your image, I mostly do but it does seem a bit gloomy in the foreground. With the specific image here, the main thing I would play with if it was me, would be to try various ways of getting a better balance between the sky and the landscape - at the moment the foreground and land seems dark given the sky conditions. If you haven't found this already, learn how to duplicate the modules so you can have two or more instances of the same module working on different parts of the image.

Learn to use it globally for the whole image, or selectively to specific areas. If you haven't already, learn the tone curve module - this will do a huge amount of the 'heavy lifting' to get the tones where you want them (whether in a colour or B&W image). There is a dedicated module called 'monochrome' for B&W conversion which you might want to try - it allows you to alter the emphasis given to different colours in the conversion, rather like you use red, yellow, green filters in traditional B&W film photography. Your B&W conversion looks pretty good to me. It is a tremendously powerful piece of software, with multiple ways of doing things, so the following is based on my experience and approach, not a definitive 'this is the right way'. I'm a Darktable user too, and have become quite familiar with it, though there are still a lot of modules I don't use regularly and I need to explore.

Recovering highlights using darktable