Finder preview pane shows black box for Canon RAW .CR2 files

I have thousands of Canon RAW photos, in .CR2 format. Finder used to show the preview image of the files in the preview pane, but now they are shown as a black box. If I resize the Finder window or resize the preview pane, then the preview image shows up temporarily. If I choose another file and go back to the first one, it shows the same black box.

Things I tried:

checked Finder VIew Options and View Preview Options, unchecked and re-checked preview box, no change

deleting and recreating the Finder preference .plist file, no change

run disk utility diagnostics on the external drive to make sure it's correct, tests succeed

This seems to have started once I updated to MacOS Sequoia 15.4. I think I should have waited for 15.4.1.