My 2TB Seagate Expansion hard drive seems that it’s HFS formatted, but it’s not writable on my MacBook Air. I can’t change the permissions. I’ve already tried to reformat it in different ways, including force-quitting mds_stores in Activity Monitor, and running First Aid a couple of times to repair it. However, no matter what I do, none works. I can drag files from it to my Mac, but not vice versa. Can anyone tell me how to add files to and edit files on the Seagate external drive?
Are you sure that your external hard drive is formatted with HFS? From your description, it seems that your drive is formatted with NTFS. NTFS is read-only on Mac and the permission for NTFS drives cannot be changed to read-write in Get Info.
To write to an NTFS external hard drive on your Mac, you need to use an NTFS driver like iBoysoft NTFS for Mac. This tool can automatically mount the connected NTFS drives to full read-write mode on your Mac. Then, you can copy files to the NTFS drive on your Mac like a local drive.
Download iBoysoft NTFS for Mac to write to your NTFS drives on your Mac now!
Since you say you can copy files on the drive to your Mac, it means that the drive is not corrupted. You can check the file system of the drive in Get Info or Disk Utility. If it is an NTFS drive, you can’t write to it. You can either use an NTFS for Mac tool to make it writable on your Mac or back up files on it and then reformat the drive to exFAT, APFS, FAT, or HFS+. All these file systems are compatible with macOS.