iCloud & iCloud Photos · iCloud Drive basics
Can I stop iCloud Drive syncing one folder?
Short answer: Not directly: iCloud Drive syncs everything inside it and has no official per-folder exclusion. Move the folder out of iCloud Drive (and out of synced Desktop and Documents) to another home-folder location or an external drive.
Not directly — iCloud Drive syncs everything inside it, and there's no official way to exclude one folder. To keep a folder local only, move it out of iCloud Drive (and out of Desktop and Documents, if those sync) to another folder in your home folder or to an external drive.
The opposite — keeping a synced folder always on your Mac — is possible with Keep Downloaded; see keeping an iCloud folder downloaded.