I believe this is incorrect. Systemd-networkd handles layer-3 routing and some amount of layer-2 stuff (MAC addresses, etc), but it doesn't handle wifi connecti

I believe this is incorrect. Systemd-networkd handles layer-3 routing and some amount of layer-2 stuff (MAC addresses, etc), but it doesn't handle wifi connections. Wifi connections are handled by wpa_supplicant (the older, and still more common wifi daemon) or iwd (newer, but not yet widely adopted). The vast majority of users control wpa_supplicant indirectly through NetworkManager, so it's not widely known that it can be configured using simple text files. But it can! On Arch linux, the default config file location (for network card wlan0) is: /etc/wpa_supplicant/wpa_supplicant-wlan0.conf. iwd is similarly straightforward to configure using text files. Using the CLI front-end is typically a nicer experience, since you get to pick the SSID from scan results and you get quick feedback if you mess up the password. But if you want to do it manually, just create one file per wifi network (containing SSID, password, etc) in /var/lib/iwd/.