I need the link to dowloand Photoshop 2020 (versión 21)

Hi @antonella_9609 that version of Photoshop is no longer available to download at all. The earliest version available is 22.2 (to support legacy 3D) otherwise the only versions available are the current and one year previous. 

Be warned - people will post or reach out stating they have a link - those are considered malicious. There are no valid direct link downloads.