MacOS Tahoe seems to have disabled external drives.

If you have 3rd party ‘protection’ software installed, that may be the problem. For example, ESET has been reported to prevent external drives and memory cards from mounting. Such 3rd party system ‘helpers’, ‘cleaners’ and ‘protectors’ do more harm than good. In fact, such products are completely unnecessary for macOS and the only‘good’ (if you want to call it that) they do is to put money in the developers’ pockets. For the user, they offer only harm…and if that is limited to harm to your bank account, then count yourself lucky.

Given that it mounts in Safe Mode (which would disable things like ESET), I suspect something like that is the culprit, but…

If you have a Mac laptop computer (not applicable to Mac desktops), accessories must be allowed to connect. Go to System Settings > Privacy & Security > Accessories, try changing it to Automatically allow when unlocked or Always allow.

There were a few prior posts on this forum from users who couldn’t access their external drive due to the drive manufacturer’s software that they used to encrypt the drive. Lacie/Seagate, Samsung, SanDisk, etc., all provide 'drive management' software on their drives and using such 3rd party software can cause issues when macOS is updated and the 3rd party software becomes incompatible. Not sure if that's theissue here, but FYI the best practice with a new external drive (SSD/HDD, not applicable to NAS drives) is to use Disk Utility to complete erase it, format it as GUID/APFS and apply encryption if desired.

Harlequin_Witch13 wrote:

However, I will check the security program settings and see if there is something I can correct.

since there are "security program settings", and also you stated that you bought the drive because of "compatibility". that tells me you are using manufacturer's bundled software

when you use software from just about any manufacturer for their storage device you run the risk of that same software not being compatible with macOS updates / upgrades. it can cause the software to stop working. at best this will cause you a headache. at worst it can render your data inaccessible. it is always best to use disk utility to erase and format a drive before use to remove any preloaded software.

if you are using such software, i think your options are somewhat limited. 

you may want to contact the manufacturer and see if there is an update for their software.

alternatively, if you have a backup you can revert your macOS to the version of macOS that the drive was working on and transfer your data to another storage device and then erase and format that specific device before putting it back into service.

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

Harlequin_Witch13 wrote:

Updated my Macbook Pro to macOS Tahoe and now it will not recognize my external hard drive. I have checked that the drive is still viable by connecting it to both my iPhone and my iPad. When I boot my Macbook in safe mode, the disk utility is able to recognize and mount the drive but, in standard operating mood, my external drive simply does not exist within finder and will not mount via Disk Utility or the Terminal commands.

Is there a patch in progress to fix this error as I am well aware that there are others experiencing the same issue?

I emphasize, the drive has not failed and was completely visible and able to connect before the OS update. This is absolutely an issue with the OS.

Do you have some form of NTFS software installed. It might have come bundled with the drive. When that software breaks, it prevents mounting of any external drives that are formatted in any sort of Windows file system.

Please download and run Etrecheck.  The free version is sufficient. However, if you find it worthwhile you should support the developer and purchase the app.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and after clicking on the Reply button use the Additional Text button to paste the report in your reply.

Then we can examine the report and see if we can determine the cause of the problem.

Barney-15E wrote:

Start up in Safe Mode and see if the drive is recognized.

The OP stated (in the original post) that the drive can be mounted in Safe Mode. That pretty clearly indicates the problem is with some sort of 3rd party ‘protection’ crapware.

Glad that sorted it. FYI, that ‘security software’ is unnecessary. If it’s something mandated by an employer, then I can understand. But otherwise, I’d recommend uninstalling it.

Harlequin_Witch13 wrote:

The drive was formatted when I first got it to ensure proper compatibility.

Compatibility with what?

It was working fine up until the latest OS update.

Well, that’s to be expected with third party crapware.

Start up in Safe Mode and see if the drive is recognized.

Start up your Mac in safe mode - Apple Support

However, I will check the security program settings

Oh, it gets worse?

neuroanatomist wrote:

Barney-15E wrote:

Start up in Safe Mode and see if the drive is recognized.

The OP stated (in the original post) that the drive can be mounted in Safe Mode. That pretty clearly indicates the problem is with some sort of 3rd party ‘protection’ crapware.

Yeah, and I didn't get any positive feedback on having installed anything, so I pressed the issue in a different way.

I really hate when people try to butt into my conversations. I really don't care what anyone else has contributed.

Harlequin_Witch13 wrote:

When I boot my Macbook in safe mode, the disk utility is able to recognize and mount the drive...

Barney-15E wrote:

Start up in Safe Mode and see if the drive is recognized.

I really hate when people try to butt into my conversations. I really don't care what anyone else has contributed.

I really hate when people try to tell others what they should or should not post. I also really hate when people offer 'advice' that clearly shows they failed to read information that OP provided when asking their question. I guess we all all have pet peeves, and maybe the best course of action would be to try and help the OP.