I don’t fully understand it, but I believe the way to think about it is that: we never “see” something fall into a black hole. But the photons from the “last moment we see” get so redshifted they’re essentially invisible. Therefore from a reasonable distance it “looks” like the object disappeared and the event horizon grew in size.

Here’s a video, he talks about the redshift around the 8 minute mark. https://youtu.be/vNaEBbFbvcY