Comment by bluebarbet

For years I have been syncing with great success using the most basic FOSS tools: `rsync` over `sshfs` on desktop, and SSHD (via an app called Dropbear available on F-Droid) on mobile, using an ad-hoc network over the wifi hotspot (which is turned on by Macrodroid - alas not FOSS - when the device is plugged in). This setup is rock-solid reliable and very fast.