Hi @Giorgos Bakolas ,
Unfortunately Microsoft only keeps the last three (3) versions of the Remote Desktop client available for download on their official pages over here:
https://learn.microsoft.com/en-us/windows-server/remote/remote-desktop-services/clients/windowsdesktop-whatsnew
Your best shot is to use your favourite search engine and look for someone that may have a download link (unofficial) or then you could consider contacting Microsoft support and check if they may be able to provide you the version you're looking for.
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Best regards,
Leon