Lightroom classic v11

You will find that the CC Desktop App only allows a downgrade to the one previous version. (Currently only v13.nn and v12.nn are available).

You might be able to contact Adobe Support and request v11. Be aware that catalogs are not backwards compatible.

Contact adobe support by clicking here, https://helpx.adobe.com/contact.html?rghtup=autoOpen
In the chat field (lower right of screen), Typing “Agent” into the chat text field will bypass the initial chatbot.
If you are not able to get to the chat window, then disable your ad-blockers, firewall, enable cookies/scripts on your browser. If it still fails then change your browser/machine/network.