m-law
You should be able to use the file CLI to migrate from one backend to another: eg. php manage.php file migrate --backend=3 --to=D
If that gives you too much trouble, since your end goal is to go from S3 to FS you should be able to simply dump the entire bucket via S3 CLI, move that to a folder on the FS, unpack it, and then connect the plugin instance to that folder. Now you will need to ensure the webserver user (or php-fpm) has appropriate read/write access.
Why this works is because we use the same folder structure with S3 that we do with FS. Each file is stored in a folder that matches its first character (so if the file key is xHSbsw68eu.. then it will be stored in x/). On Linux this is all case-sensitive (meaning x… will go to x/ and X… will go to X/) but with windows FS it’s not (meaning both x… and X… go to x/) so just be careful with that.
Cheers.
