I am not sure what the at-scale energy use reduction of this bug fix will be, but...
If I had a pile of money I would consider creating a special bug bounty style program for energy use reduction.
This might be a very efficient way to reduce carbon output from personal and data center computing.
The staff at a metal-recycling company we were installing at, started complaining that the furnace would stop optimizing overnight. We investigated.
The controller computer would go into power-save mode, which suspended our control app. So the furnace would just sit there wasting power and burning up electrodes.
I calculated that during that week our furnace site wasted more power than all the power saved in America that year with power-save mode.
It would literally have been better if they'd never invented power save mode.
So be careful how much fiddling around we do. The law of unintended consequences will bite you in the butt every time.
Only if you considered the purpose of power-saving mode to reduce total energy usage, vs to reduce amount of power (and consequent wear & tear) an individual machine uses. However that MS would release a feature like that which automatically kicks in on upgrade without any sort of consideration of what the machine was used for - it could be running life-support systems! - seems an issue. But I'd also expect a fair bit more diligence on behalf of engineers responsible for monitoring and maintaining systems that need 24x7 uptime.
Life support systems don't run windows. And if you're running consumer windows on anything critical, you fucked up.