subscription, you can check for older versions directly in the app: Open the Creative Cloud Desktop App. Locate Photoshop in the "All Apps" or "Installed" section. Click the three dots (...) next to the "Open" or "Install" button. Select "Other Versions"
If you cannot afford a perpetual Creative Cloud subscription (though note Adobe no longer sells perpetual licenses after 2017), there are legal workarounds: adobe download photoshop 2020