After Norton Utilities Premium was updated a few days ago I found that I had the same problem described in "Norton Utilities Changing Power Plan", viz., I could not change the Windows 10 power plan.
When I followed the advice at the the previous post by toggling the "Power Optimizer" to off in the "Real-Time Boost" section I ran into a problem. I was able to then choose the "Balanced" power plan. However, when I put the computer to sleep via the Windows menu, closing the laptop lid, or letting Norton set sleep after a Quick Scan, the computer would not sleep. I discovered this by closing the lid and putting the laptop in a carrying bag. Hours later when I went to use it, it was very hot and the battery was dead. Further, I had to do a hard reset to get the computer to reboot.
Thereafter, no matter how I set sleep mode, I could not wake the computer, a Lenovo Flex 5 laptop. I would always have to hard reboot it, i.e., by holding the power button for several seconds.
I finally turned the Norton Utilities "Power Optimizer" back on and the computer's sleep ability seems to have been restored.
I am using Norton Utilities Premium, version 21.4.5.428
I have tried to turn the "Power Optimizer" off and then select the "Balanced" power plan. This has resulted in the "no sleep" problem.
For now, I have the "Power Optimizer" turned on and I can select "Balanced". Other times, when I select "Balanced" my choice will be overridden and the Norton option will be selected.
There are a set of settings someplace which I am missing. For now, my computer will sleep. However, I am concerned that Norton Utilities has overridden my ability to choose in such an opaque way.
Thanks. That was enough for me to find the setting.
For anyone finding this thread in the future, it's not well designed- the toggle for that setting is actually in a different location than you would expect.
For clarification, the core issue was the app was changing the laptop's power plan, which in turn would shut my pc down after a set time. There are many reasons to leave pc on, and it was vexing me.
Open Norton Utilities, Go to Real Time Boost section on the left, and then on the right select the Processor section and click on the Power Optimizer button to toggle it. I say it's not clear because that tab/page appears to deal with CPU settings, whereas the Configuration tab that has the Power Plan choices (just not one to say 'no thanks') does not provide a way to turn it off. I feel the Power Plan option to toggle this feature should be on the same page as the other settings.
In fact, the only way to confirm that button on the Processor page is actually controlling the Power Plan is to toggle it and then go to the Configuration tab and note you can not select a drop-down choice for Power Plans.