FWIW, I asked my physicist friend this question one time. He said while an outside observer would never see a "massless test particle" enter the event horizon

FWIW, I asked my physicist friend this question one time. He said while an outside observer would never see a "massless test particle" enter the event horizon due to time dilation effects, real particles have mass and their own gravitational field, and thus due to complicated stuff they can eventually been seen passing through or otherwise somehow merging with the event horizon.