Pi Zero 2 W - Ubuntu Server headless wifi setup - modify /etc/netplan/50-cloud-init.yaml

50-cloud-init.yaml

# This file is generated from information provided by the datasource.  Changes
# to it will not persist across an instance reboot.  To disable cloud-init's
# network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    ethernets:
        eth0:
            dhcp4: true
            optional: true
    version: 2
    wifis:
        wlan0:
            optional: true
            access-points:
              "SSID":
                password: "PASSWORD"
            dhcp4: true

https://linuxconfig.org/ubuntu-20-04-connect-to-wifi-from-command-line