The water is quite hard here, about 360 mg/l (ppm). I use anhydrous citric acid to descale my washing machine once a year, which seems to work well enough, although I do have a bit of limescale in the folds of the seal. It is 16 years old though, and I didn’t descale it for the first few years, until it started causing elements to fail and blocking and jamming the coin trap! Not having a softener does of course mean I need to use a lot more detergent powder.
I have seen advice that softened water may promote corrosion of aluminium spiders, in fact a friend was told that too, when his 2 year old machine failed, but I’m not sure if that’s correct. The main causes I’m aware of are bacterial related.
You can get manual water softeners, which sort of resemble a fire extinguisher and are usually used with warewashers, but a washing machine would presumably use a great deal more water, so not sure you’d get a worthwhile number of cycles out of a modest sized one, between needing a manual recharge with salt and a flush.