Some doors have this plate that guards the latch mechanism.
For some reason my search-fu is failing, I found tons of diagrams of lock and door parts but I can't find that plate.
What is that called?
One match is "Latch Guard":
The protective plate around the keyhole in a door is called an escutcheon plate, but the term can be used to describe a metal plate serving a similar purpose, either protecting a mechanism or a surface or finish, on architectural fittings like doors and windows as well as on furniture. Hope this is somewhere close to useful.
If the plate went the entire height of the door, it would be called an Astragal.
The best citation I found for this is Oxford Languages (Google's dictionary search partner), but there is no link.
noun: astragal; plural noun: astragals a convex molding or wooden strip across a surface or separating panels, typically semicircular in cross-section. ARCHITECTURE a small semicircular molding around the top or bottom of a column. a wooden molding that covers the gap between a pair of doors or casement windows. a glazing bar, typically one used in cabinetmaking.