Wave-particle duality doesn't mean that light is sometimes a wave and sometimes a particle, it means it's a third thing that has some things in common with both waves and particles

When we're measuring light passing through diffraction grating, it's most useful to treat it like a wave. When we're discussing the photoelectric effect it's best to treat it like a particle.

A good analogy I read in a reddit comment that I can no longer find: wave-particle duality as a concept is like if you saw a train and described it as exhibiting "horse-house duality", because it's sometimes like a horse in that it moves around and takes you to places, and sometimes like a house in that you can sit inside and it protects you from the elements. But you know it isn't a horse or a house, it's a third thing. If you're solving a question about how long it takes to travel somewhere you might model the train as being like a horse. If you're solving a question about how much stuff can fit inside of it, you might model it like a house. But you know neither of those are actually the truth.

All particles have wave-like properties. But for particles of fairly high mass, those wave-like properties are so small that it's easier to ignore them.