iCloud & iCloud Photos · Online-only files and Optimize Mac Storage
How do I bring an online-only iCloud file back onto my Mac?
Short answer: Open it and macOS downloads it, or right-click it in Finder and choose Download Now (Keep Downloaded keeps it local afterwards). Storage Studio's online-only steps never move or rename the file, so nothing else needs undoing.
Just open it — macOS downloads it automatically. To download without opening, right-click the file or folder in Finder and choose Download Now; on recent macOS, Keep Downloaded also keeps it local from then on.
Nothing else needs undoing. Storage Studio's online-only steps don't move, rename or delete the file, so once it's downloaded it's exactly as it was, in the same folder.
Make sure you're online and have enough free space for the download.