Debian stretch 9.4 is ARM 64 bits, currently needs some configuration (automount uSD, change hostname, CLI Bluetooth device configuration, touchscreen as touchpad), but itsn't 100% operational as 3G/4G doesn't work (only WiFi and Bluetooth) and there are some softwares with too small fonts (Gnome one's ?), like Synaptic, IDLE, Geogebra, etc.