WiFi/ssh on headless BPI -M2M (16.04 serv '21)

Hi, I installed the Ubuntu 16.04 server version from 2021. Booting the BPI-M2M takes a few seconds, then red and blue LEDs are constantly on, and the green LED blinks. This is fine, I guess. But how can I configure the WiFi and ssh access? My board is completely headless. I tried the NanoPi instruction http://www.alvaroferran.com/blog/headless-really-wifi-and-ssh-setup but without luck. Which configuration files should I edit (and how) for a simple WPA (ssid+password)? Best, Robert