[RedDevil]

The big problem with using exhaust heat to power anything is not so much in aquiring the heat - it is right there - but shedding it on the other side of whatever device you'd use.
As you cannot power anything with just heat. You need a temperature differential.

Take the simplest form: Electric energy directly from your exhaust. Attach a Seebeck effect element between the exhaust pipe and a big metal plate. That will easily produce several Watt of electricity that you can feed back into the 12V system. Great!

Except that the plate needs to be quite big to shed enough heat to make it work effectively. And you cannot just attach it to the car body; you do not want to heat that up. The exhaust pipe trajectory is not isolated for nothing.
All in all you'd add quite some weight to the car, just to get a few Watts, less than 0.1% of whay you'd use on the highway. ROI? Not in a lifetime.

The same applies for other approaches; the Stirling generators, the steam turbines; they all need cooling, and that's where it stops being practical for cars.

There are stationary applications that produce heat 24/7. Weight is not an issue there. Size is generally not an issue. They work all the time. They could use waste heat for power generation so much better than any car ever could.

But they don't generally. There are exceptions, but they seldom get a follow-up.
There must be a reason for that.
The reason is that even in ideal circumstances the power generated hardly makes up for the initial cost and maintenance, if at all.
If it does not work there, it has no place on a car. Sadly.