raspberry pi 4 wifi setup using command line only – bash

• find the wifi adaptor name

lshw

ls /sys/class/net

it was wlan0 in my case

• edit /etc/netplan/50-cloud-init.yaml

network:
    ethernets:
        eth0:
            dhcp4: true
            optional: true
    version: 2
    wifis:
        wlan0:
            optional: true
            access-points:
                    "SSID-NAME":
                            password: "your_password"
            dhcp4: yes

• Test the config

netplan try
netplan --debug try

This command will make the above changes for 120seconds if anything wrong it will be reverted back. OR you can hit Enter to make the changes.

• apply config

netplan generate 
netplan apply

#enable wifi module

modprobe brcmfmac

#disable
modprobe -rv brcmfmac


nano /etc/modprobe.d/raspi-blacklist.conf

blacklist brcmfmac
blacklist brcmutil

More : https://raspberrypi.stackexchange.com/questions/108636/setting-wifi-up-via-the-command-line-ubuntu-server-18-04-4-lts-raspberry-pi-4

https://huobur.medium.com/how-to-setup-wifi-on-raspberry-pi-4-with-ubuntu-20-04-lts-64-bit-arm-server-ceb02303e49b