How do I stop work alertness from bleeding into my whole life?

You trained yourself to stay alert because the work demands it, and now that alertness will not switch off when you go home. The very vigilance that makes you good at your job is following you into dinner, into sleep, into the parts of life that are supposed to be safe. That is a common cost of the work, and it is worth taking seriously. The mind does not have a separate setting for on the clock and off. If you run it in threat-detection mode all day, it stays there. The goal is not to care less at work. It is to teach your nervous system that not every moment is a moment of danger, so it can stand down when there is nothing to defend. So build a real edge between work and the rest. A short ritual at the end of the day that tells your body the watch is over. Time where notifications cannot reach you. When you notice the scanning starting at home, name it: there is no threat here, I am off duty. You are not lowering your guard on the job. You are giving the guard permission to rest so it lasts.