How do I control which Desktop files and folders are automatically backed up to iCloud on my Mac?

A previous post asked this question & got 2 answers, both of which missed the point. The objective here is for me to control what files and folders get copied to iCloud, instead of having the Mac automatically keep a copy of everthing on my desktop. As the previous question tried to make clear, this seems like a sneaky way for Apple to force users to buy a subscription that increases their available iCloud storage space. If I could manage for myself what gets backed up to iCloud I could control the storage space so that I wouldn't have to increase my iCloud capacity. Note, when I go to settings and try to manage this automatic syncing to iCloud I get a nasty message telling me that if I proceed then some files and folders will be "deleted from my Desktop", but kept on iCloud. That's exactly the opposite of what I want, which is to have control over what Desktop (and other) files and folders get synced to iCloud, but to keep everything as is on my Desktop. Can someone please advise me re- how to do that?

[Re-Titled By Moderator]