External drives · Choosing a drive
Can I use iCloud Drive or another cloud account as my fast drive?
Short answer: No — the fast drive must be a physical external drive, since moved apps and folders open straight from it. Use cloud accounts through Data Transfers, and keep cloud files online-only, to save space with the cloud.
No. The fast drive must be a physical external drive attached to your Mac, because moved apps and folders are opened straight from it and need it to answer instantly. Cloud storage doesn't work that way.
The cloud still has a role in Storage Studio: connect your accounts and use Data Transfers to copy, move or sync files there, and keep downloaded cloud files online-only to save space. See Cloud accounts.