My Windows PC locks itself when I walk away, and I didn't install a thing to make it happen

My favorite Windows features aren't the grandiose ones that let you do a bunch of stuff in one sweep. What impresses me are the ones that do one particular thing, no matter how minuscule, well. Often, these are things that you didn't know you needed, but living without them becomes impossible. One such feature is Dynamic Lock. I went years without knowing it existed, despite it serving a genuinely useful purpose for my use case: it automatically locks my computer when I'm away from it.