I never got to use this, so I can't really give much input. I'd imagine they took this away to prevent an inconsistent 120Hz with the CPU being locked down to 70%, as well as saving as much power as possible.
Hello @Litt ,
We do have other members who like the ability to have adaptive 120hz refresh rate with battery saver on.
Unfortunately our R & D has decided that it is not the best option for battery savings.
One UI Beta Team