Are you sure you want to quit all applications and log out? Pops up randomly

My 2019 MacBook Air has developed a habit of either shutting down or restarting all on its own. However, if I have a Word or Excel file open and unsaved, it will stall at the dialog box asking me if I want to save before quitting. It usually happens when I am away from the screen for periods of minutes to hours. If I'm gone long enough, there will also be a dialog box informing me that my Mac failed to restart because of open applications. So, why is it trying to restart on its own? I don't have automatic update/install configured. I usually run Safari, Mail, Office 365, 1Password. Looking at a previous poster on the topic, a few people replied with standard info about how to shut down, etc. That's not what I'm looking for. I'm not trying to shut down; the laptop is doing it unbidden, and there is no app openly trying to subvert me.