Unable to open files in external device

If the file system on the Seagate drive is NTFS, then macOS can only read an NTFS by default. If you need to write (including delete) items on an NTFS volume, then you need to install the Seagate proprietary software or purchase a third party NTFS driver.

However, the preferred option is to avoid using the NTFS file system on a Mac. Instead use a file system which macOS actually supports. MacOS Extended (Journaled) and APFS are the best options if the drive will only be used with Macs (which of these two file systems to use depends on the type of drive and which Macs need access to it). If the drive will be shared with Windows, then use Disk Utility to erase the whole physical drive as GUID partition and exFAT.

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

If you are using an Apple file system, then make sure to check "Ignore Ownership" in the "Get Info" of that drive.

If you don’t have permission to use files on a Mac disk - Apple Support

if that is a Time Machine drive, MacOS prohibits deleting or modifying its individual files.