Seagate External Hard drive not reflecting free space

citylover wrote:

What do I need to do?

You need to avoid using Time Machine drives for anything other than Time Machine.

Can you explain how you configured this drive? While you definitely should never share Time Machine drives with other data, Apple did make the process slightly easier/harder. I can't say which.

It's possible that if you had created a separate volume of your manually copied files, then you may be able to just remove that volume and recover the space, but no guarantees.

If you didn't create a separate volume (or maybe even if you did), then your files may still be remembered in a Time Machine local snapshot on the drive. If so, then they might go way when Time Machine automatically cleans out old snapshots. But that would only be due to random luck. There is one sequence where Time Machine may not delete the files until the entire drive gets full and it starts deleting old backups.

All of this is a guess. I don't really know and I'm not going to experiment. There does exist a guaranteed solution. Erase the Time Machine drive and don't do that again.

I will strongly second etresoft's remarks and add the comment that only Disk Utility is able to accurately show available space.