Arc Sync
The Arc Sync feature provides end-to-end encryption for your sidebar across your devices that is fast and doesn't depend on iCloud. This cross-platform capability is a step towards Arc anywhere; iCloud sync was phased out since it's Apple-specific, and Arc is now on Windows (and Android soon).
Setup
Click the "Sync Sidebar" in the Arc Max tab of Arc > Settings (Cmd + comma), just below the Sync Sidebar with iCloud setting.
