According to Apple, Low Power Mode on Mac reduces the system clock speed and the display brightness in order to extend your battery life even further. This means that if you're doing less intensive tasks like watching videos or browsing the web, you can eke even more out of your Mac's battery.
It goes to show how much display brightness can impact your battery life.
Even if you're not running Monterey, turning your display brightness down as much as you can while still maintaining screen readability should help you get a lot more life out of your Mac's battery, I've found. The same goes with pretty much any device that uses a display. Even the old iPod Classic had the option to adjust its display brightness—a feature which likely also helped improve battery life to some extent.