For regular fuse/FAT file system type, there is no need to preserve file permissions, just copy all files as usual. You can check file system type by typing in mount in the terminal emulator. You will see somthing like this example:
/mnt/media_rw/149B-8301 type vfat
/storage/149B-8301 type fuse
149B-8301 is the UUID of the SD card and it shows that the file system is vfat.
To copy files regularly, run the following:
adb pull -a /storage/149B-8301 ~
advanced copy (tarball archive)
adb exec-out "tar -c storage/149B-8301 | gzip" > ~/sdcard_backup.tar.gz
copy from PC MicroSD Card Reader
cd /media/xubuntu
tar -czf ~/sdcard_backup.tar.gz 149B-8301
Note: replace ~ with path to target disk drive providing enough free disk space on PC