I've had the same problem with Lightroom ver 9.1. It first happened with a new memory card shooting Raw, but it also happens with 2 other cards and jpg images. The cards are easily read with iMacs Finder and I have copied images to a folder and then imported into LR, as a temporary measure.
What version of Lightroom did you install and what version did you come from? Lightroom CC does not exist anymore. It is either just Lightroom (for the cloud version) or Lightroom Classic(for the version that stores images locally).