No RAW (CR2) thumbnails showing in Finder

Hello - I'm using a Canon 5D Mark 4 Camera. I always could see little preview thumbnails of the RAWs in the Finder. Since two days I can't see them anymore, I haven't changed anything.

I already checked, that "show icon preview" option is activated.

Hope you can help, this is so frustrating!

By the way the RAWS of a sony A7III are shown as thumbnails. Don't get the problem with the CR2 files.