Mild hybrids are just that: slightly electrified ICE cars. They’re cheap to make; the current preferred tech is a 48v motor/generator replacing the alternator, often belt driven, and a slightly higher capacity 48v battery replacing the 12v system. You can do start/stop when the car isn’t moving much more smoothly, and use the motor to fill out a little bit of parts of test cycles where ICEs are very inefficient, as well as do a tiny bit of regeneration. It also gives you power to electrify other accessories if you want. The benefit is maybe 10-15 percent improvement in economy for very little cost, just a few hundred dollars. The German luxury makers are all doing this on almost every model, and there’s increasingly a 48v electrical component market evolving, so you don’t have to do much DC/DC conversion to run 12v stuff. And 48v is below the 60v safety limit, so you don’t have to have special electrical certification to work on a vehicle in the EU.