rtl8723du is already supported in the main rtl driver. I found this out the hard way, eventually.
From https://www.reddit.com/r/raspberry_pi/comments/ohdm7y/nano_usb_wifibt/
With some hints from https://forums.linuxmint.com/viewtopic.php?t=304266&start=20 I was able to use lsusb to find the device identifier, then modprobe -c|grep -i 7392|grep -i a611 to find out that it is included in the rtl8xxxu driver, which I then discovered is disabled by default in /etc/modprobe.d/blacklist-rtl8xxxu.conf so it is just a matter of removing the blacklist to re-enable the driver and a reboot and wifi is working!
TLDR: run this in a root terminal echo "" > /etc/modprobe.d/blacklist-rtl8xxxu.conf && reboot