solution - spend $80 and get a new battery.
It has nothing to do with the battery, the slow down is hard coded.
Under $20 if you install your own, including tools.
Doesn’t slowing down any battery operated, computerized device make it run longer between charges, a way to extend life of old batteries?
I thought about that. My iPhone 6 was sluggish after the last upgrade, and I had noticed more rapid battery drain before that.
Batteries drain and chemistry degrades. A new battery would have given it new life, but technology marches on. The new camera and cpu/gpu tech among others prompted my to upgrade to an iPhone 8.
If I only relied on phone and maybe browser functions, I wouldn’t have bothered. But it’s a tool. A sophisticated one at that, and the newer hardware appeals.
My $0.02