The whole documentation is on GitHub:
The release notes are here:
https://github.com/docker/docs/blob/main/content/desktop/release-notes.md
You can list the history of the changes and go back to a point when that version still had a link. For example here:
Then you will find something like this:
{{< release-date date="2023-06-05" >}}
{{< desktop-install all=true version="4.20.1" build_path="/110738/" >}}
You will need the number in the “build_path”. Then copy a download link in the documentation and remove the part after the question mark so you see the whole url more easily. You will have something like this:
https://desktop.docker.com/win/main/amd64/149282/Docker%20Desktop%20Installer.exe
Now Replace the number after the architecture in the URL with the build number of Docker Desktop 4.20.1
https://desktop.docker.com/win/main/amd64/110738/Docker%20Desktop%20Installer.exe
This is a link for Docker Desktop for Windows.
Note that there is no guarantee that older versions will work properly on current systems and there is no support for those versions.