Mercedes V6 Hybrid Formula One engine

It idles at 5000 rpm !
https://en.wikipedia.org/wiki/Mercedes_V6_Hybrid_Formula_One_engine

Has a kinetic energy recovery system. Stores some of the energy otherwise wasted during braking, storing it electrically ior by flywheel, I'ld prefer electricity, toyota use a super capacitor
https://en.wikipedia.org/wiki/Kinetic_energy_recovery_system

Also a heat recovery system.
Like a turbo the exhaust gases drive a turbine that makes electricity, this spins the turbo at low revs, eliminating 'spool up' time for turbos
https://f1.fandom.com/wiki/Motor_Generator_Unit_-_Heat#:~:text=Edit,also%20functions%20as%20a%20motor.