iCloud & iCloud Photos · iCloud on the web, Windows and other apps
Can I use iCloud Drive and Dropbox or Google Drive on the same Mac?
Short answer: Yes — each syncs its own folder. Don't nest one service's folder inside another's, and avoid keeping the same files in both, which doubles the space used in the clouds and on your Mac. Make files online-only to save Mac space.
Yes. Each service syncs its own folder and they don't conflict, as long as you don't put one service's folder inside another's. Avoid keeping the same files in both: that uses space in both clouds and twice on your Mac if both keep local copies.
To save Mac space with several clouds, make their files online-only. Storage Studio can do that for iCloud Drive directly; other providers depend on their own apps — see why iCloud frees in one step.