I recently bought a USB Stick to expand the storage on my mi box, but it does not have the permission to write on it. I have also setted it as system storage, but apps like Kodi won't be able to write data on it. Tried to move a 200mb file on the "expanded" storage and it worked (has only be moved to internal storage) und I also tried to move a 3000mb file, but this did not work.
So is there a way to move any file to the USB Stick which is connected to your Mi Box S?
Your description is kinda confusing. Are you using your USB drive as "Device storage" or "Removable storage"? You can find out under "Storage & reset" in settings, like this:
https://i.imgur.com/yEnTmJv.jpg
USB drive used for "Device storage" is mounted as "/sdcard", which can expand storage for apps but can't be used on PC anymore. "Removable storage" is mounted as "/storage/XXXX-XXXX", which can be used on PC but can't be written by default on Mi Box. However, you can enable "Use X-plore USB Driver" in X-plore settings to write to "Removable storage" formatted with FAT32. Similar USB OTG settings in MiXplorer allows you to write to FAT32 & exFAT.
https://i.imgur.com/NoErsxl.jpg