For my reference in the future I will record here the steps that I had to follow in order to install Openwrt on the tp-link router EX220. This was done using a Windows 11 machine.
Disclaimer: Use this tutorial at your own risk. We are not responsible for any damage/harms done to your device using the information from this tutorial.
These are the steps provided at the official https://openwrt.org/toh/tp-link/ex220_v1 page: