Apple announced its new operating systems for 2021 this week at WWDC and a few tidbits have come out in the past few days, one of them is the addition of Lower Power Mode to macOS Monterey and iPadOS 15, marking the first time the feature has moved beyond the iPhone since the feature was introduced.
Low Power Mode came to the iPhone in 2015 with iOS 9 and throttles the CPU back, dims the display, disables background app refresh and mail fetching to help preserve battery life. On the iPad, with iPadOS 15 it will work in the exactly the same way.
On the Mac however, it works on MacBook and MacBook Pro notebooks manufactured in early 2016 and later but not the MacBook Air. Lower Power Mode in macOS will work when the Mac is plugged in or on battery.