Unable to connect Seagate Backup+ Hub to 2019 iMac on Sequoia

If you previously used Seagate's proprietary software (like Seagate Dashboard, Toolkit, or Paragon NTFS driver), macOS Sequoia may block it or fail to mount the drive because the old software is incompatible with the updated OS. 

Try this

• Check for custom security: If your drive is encrypted using Seagate software, the legacy "Unlock Drive for Mac" application will fail to launch on Sequoia. You need to download and install the latest version of seagate toolkit  to cleanly unlock the drive. 
• Uninstall Old Dashboard Software: If you aren't using password protection, the old background drivers might just be freezing the disk system. Go to System Settings, check for legacy Seagate options at the very bottom, or look in your Applications folder to run the uninstaller. Macs handle external drives natively, so this software is usually unnecessary.