It seems that there is a new ExFat driver for Linux. That is not amazing in itself, but it claims to fix a bug that causes some files written by the camera to become invisible. It appears that some cameras don't write to ExFat properly:
"Linux 5.14's exFAT brings improved compatibility with the exFAT file-systems from some digital cameras. In particular, when mounting an exFAT file-system from select digital cameras under Linux, in some cases not all of the files would show up under Linux.
This issue appears to be ultimately with the digital camera's firmware and not Linux in that the data length in the stream entry of the directory is not getting updated under some conditions. This meant Linux wasn't showing all of the files in a given directory when the data length wasn't being updated."
It seems to be mainly a problem with Fuji.