Can I decide what is backed up on iCloud from my Mac

Please keep in mind the distinction LACAllen made. Things are synced to iCloud from your Mac, not backed up. If you delete them from the Mac, they are deleted from iCloud.

If you want to back up your Mac, use Time Machine and an external hard drive.

Back up your Mac with Time Machine - Apple Support

Short answer is no.

By default the iCloud Drive folder is synced. You can choose to also sync the desktop and the documents folders.

that is all the control you get.