Cloud-Init configuration files for connecting Wi-Fi and ethernet to Raspberrypi 4B

50-cloud-init.yaml

# /etc/netplan/50-cloud-init.yaml
# Indent size = 2 spaces. No tabspaces allowed.
#
# 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: <------- {{ PAY ATTENTION TO THIS PART. This may be different for you; follow your version }}
# network: {config: disabled}
network:
    version: 2
    ethernets:
      eth0:
        addresses: [192.168.100.30/24] # whatever address you want the device to have
        gateway4: 192.168.100.255 # this has to be same on both the connected devices
    wifis:
        renderer: networkd
        wlan0:
            access-points:
                YOUR_WIFI_NAME:
                    password: YOUR_WIFI_PASSWORD
            dhcp4: true
            optional: true

99-disable-network-config.cfg

# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg
# First, disable the cloud-init network configuration by
# creating this file in the location specified above
network: {config: disabled}

after-all-that.sh

# After disabling the cloud-init network configuration
# and editing /etc/netplan/50-cloud-init.yaml
# run these commands in your Raspberrypi 4B terminal

sudo netplan --debug generate # check your file for errors
sudo netplan apply && sudo reboot # apply the new network settings and reboot

What if our wifi has no password?

As per my knowledge cloud-init only supports password protected networks. I personally have not tried connecting it to an open network yet so I can't give more information on that, sorry!