In RO context it's called remineralization (or alkalinization, I guess), not softening, and a lot of home RO systems have a final stage for it.
Googling for reverse osmosis minerals will bring you to a large number of probably fabricated claims about water pH and health that ultimately align on taste preference.
> “Remineralization is typically to enhance the flavor of the water, because reverse osmosis reduces the level of minerals in the water significantly, and some consumers prefer the taste of the water when there is enhanced mineral content,” explains Rick Andrews, of the National Sanitation Foundation’s Global Water Program. - https://www.thespruce.com/best-reverse-osmosis-systems-45868...
Googling for reverse osmosis minerals will bring you to a large number of probably fabricated claims about water pH and health that ultimately align on taste preference.
> “Remineralization is typically to enhance the flavor of the water, because reverse osmosis reduces the level of minerals in the water significantly, and some consumers prefer the taste of the water when there is enhanced mineral content,” explains Rick Andrews, of the National Sanitation Foundation’s Global Water Program. - https://www.thespruce.com/best-reverse-osmosis-systems-45868...
https://www.homedepot.com/p/ISPRING-Premium-10-in-Universal-...
https://www.homedepot.com/p/Express-Water-Alkaline-Water-Fil...
https://thewatergeeks.com/how-to-remineralize-ro-water/
etc