Finder and disk utility freezes after connecting Seagate external HD

Could a utility such as superduper or carbon copy cloner, make a copy of the drive without

unplugging it? Then if possible, the data could be restored from a clone/copy. These items

are best backed-up to have good workable copy, by one means or another, before trouble.

(Disk Utility in your Mac can be helpful to try un-mount or re-mount volumes such as

the external hard drive; yet damaged files may require other effort to resolve them.)

To work toward isolating issues and protect the Mac from whatever an external drive may

cause (damages to system and main user files) should be of higher priority. However that

is like most of us, problems arise when least expected; or when the backup tools also fail.

Sorry, haven't an idea on what to try now; I've other things happening offline, at 12:30AM.

Not sure if you could use safe mode/restart, and while the external drive is attached,

use the mac system's Disk Utility to see if you can unmount the external that way.

Once unmounted, it may be possible to re-start the mac and not have this issue.

Be sure to unplug the external before the full restart; or at some later interval so the

files may not be messed up due to this untimely dis/connection.

Other ideas come to mind, but I keep getting distractions & it's getting very late here.

Good luck & happy trails!🌞

Was the external drive formatted as HFS+ or APFS? If the drive was formatted as HFS+, then you may be able to repair the file system using Disk Warrior (paid app). I've used Disk Warrior for years to repair HFS+ volumes with great success.

If it was formatted as APFS, then you may need to contact a professional data recovery service such as Drive Savers or Kroll OnTrack both of which are recommend by Apple and other OEMS, plus the provide free estimates. Apple hasn't released the APFS documentation so that third party drive utilities can repair an APFS volume.

You should be careful making modifications to the drive as you may make it more difficult for a professional data recovery service to recover data.

FYI, If you cannot unmount a drive, it is better to restart your computer instead of unplugging a mounted drive.

It has been a while since I had to repair a disk in such a condition using Disk Warrior, but I believe it can repair some HFS+ volumes that will not mount, but there is never a guarantee it can fix every problem.

I don't know how DW is distributed these days since I just copy the app (already purchased by our organization) onto my customized macOS utility drive. I don't know if they distribute it on CD or if they provide a bootable USB drive. If you need to repair your boot drive, then you need to make sure DW ships with bootable media or instructions on how to create a bootable drive. If you only need to repair your external drive, then you can just run the app from your boot drive.