An IP rating has two digits. The first is solids, the second is liquids. In IP65, the 6 is the highest solids rating: dust-tight, no ingress at all. The 5 means protected against water projected from a nozzle from any direction — rain, wind-driven spray and hosing down.
Buyers tend to focus on the water digit and skip the dust one. That is backwards for signage. Water either gets in or it does not; dust accumulates slowly, insulates the electronics, and turns a cooling design into a heating one over a couple of years.
What IP65 does not solve is the inside of the enclosure. A sealed box in the sun becomes an oven, and a sealed box on a cold morning condenses. That is why our outdoor bulletin board pairs the sealing with a temperature sensor, an internal cooling fan and a heater, plus a control board that schedules power and adjusts brightness — and an earth-leakage breaker rated 250 V / 20 A, because an outdoor enclosure is also an electrical installation.