Optimise Mac Storage (Store in iCloud) not working

My 500GB MacBook Pro early-2015 (macOS Monterey) has 5GB of storage left. I have tried to Optimise Mac Storage so that my 350GB of documents and desktop remain on iCloud and are offloaded form the Mac (they are already uploaded to iCloud where I still have 370GB of iCloud storage remaining).

When I click 'Store in iCloud' and select Documents and Desktop along with Photos, I get an error message which states 'Your password is required to enable iCloud Photo Library'. When I follow the instructions, there is no place to insert a password. When I only select to store Documents and Desktop, it says 'Optimising' for a few seconds, then reverts to normal - nothing has uploaded.

I have tried the following:

• restarting the Mac
• manually clicking 'Remove Download' on each file - the cloud changes to the correct icon (download cloud) however nothing uploads and the storage remains the same
• deleting VPN and security scan apps like Avast
• clicking the cross to stop it from downloading any more - the upload quantity or progress has not moved at all (it should be much higher than 30GB)
• unchecking and rechecking 'optimise this mac'
• chatting with Apple Support who were unable to assist and suggested to just delete my files

Any help would be greatly appreciated as I need to use my laptop!