I have always used SFTP servers on my Android devices, with sync scripts run on my server daily to perform backups. I also transfer files to and from the devices this way.
With each version of Android, it becomes increasingly challenging. I now have a Samsung Tab7 FE with Android 11. I have spent hours buying and trying FTP servers, and none are working. Some only allow access to /storage/emulated/0, and the physical (external) sd-card is completely unavailable. After reading about Storage Access Framework (SAF), I found the Primitive ftpd from F-droid says it supports SAF, but it can only access new folders created by the Primitive sftpd app, and not the full file system.
What are workable approaches to provide filesystem access on Android over Wi-Fi, to enable unattended automatic backup and file transfer?
Edit - I am aware of ADB approaches, but as far as I know they are not unattended and automatic. I want to leave the tablet idle, connected to Wi-Fi, and have my script backup the tablet unattended at 2am.