How to Keep Your MacBook from Shutting Down or Going to Sleep when involved in multi - day processes

I am in the process of doing a Time Machine backing up my macbook pro just after a move from Catalina to Big Sur. And it is slow. I mean seriourly sleepy Snail slow. And I absolutely do Not want to stay awake for two of three days to make sure my mac doesn't go to sleep during the process. Unfortunately Energy Save does not exist in Big Sur System Preferences as it did in Catalina and before. This is a problem. BiG problem. I looked everywhere in System Preferences. I looked in Displays, Startup Disk, Users & Groups. Everywhere. Nothing. In 5 hours I have been able backup 17% to Time Machine. Can anyone help.