LEADTech
You have to reformat the user data partition into a filesystem, that windows can read/write to. Like ExFAT, NTFS or BTRFS (drivers for btrfs are on the boot partition of batocera).
You can do this either within batocera (system settings, developer, format a drive) or within windows (there are several tools for that, just google it).
Be aware, that when formatting a drive, all data get lost, so don’t forget to make a backup of all important files.
And be aware, that certain filesystems come with certain capabilities and limitations, see wiki for more information:
https://wiki.batocera.org/batocera.linux_architecture#using_an_alternative_filesystem_for_userdata
