Regenerative braking only works if there is spare battery capacity to absorb the energy. In general that requires a large battery to be useful. A normal car battery is nowhere near large enough and is generally topped off by the alternator.

My ICE car has regenerative braking as well, but I certainly didn't buy it for that, nor have I been able to discern the impact of it. I have driven EVs before and the regenerative braking is unmistakable.