That is expected, and mostly the point of S3/R2 is that you don’t need to back the stuff up. But there is a hidden setting that will download all of the images from S3 and put them in the backup.
Oh, but you do have DISCOURSE_INCLUDE_S3_UPLOADS_IN_BACKUPS: true.
So maybe R2 doesn’t work as originally suggested. I thought I’d tested and had it work, but I didn’t try downloading images to the backup and I likely didn’t try doing a restore or downloading a backup file.
This probably belongs in that other topic since it seems to contract the “maybe it works” hypothesis presented there.