Toshiba external hard drive not opening on my MacBook Air after macOS Tahoe update

Try running Disk Utility First Aid on the physical drive followed by the hidden Container. Within Disk Utility you may need to click "View" and select "Show All Devices" before the hidden Container & physical drives appears on the left pane of Disk Utility.

Even if the First Aid summary reports everything is "Ok", click "Show Details" and scroll through the report to see if any unfixed errors are listed since the First Aid summary has been known to lie. If there are any errors, then run First Aid again until they are gone.

chrystel1 wrote:

I opened the external hard drive in safe mode and it worked! 🥳

Most likely you have some third party software installed which is interfering with the normal operation of macOS. Typical culprits are anti-virus apps, cleaning/optimizer apps, and third party security software.....none of which are needed on a Mac. If you have any of these types of apps installed, then uninstall them by following their developer's instructions.

Did you install and run any of the software the may have come with the drive? If so uninstall it and all of its supporting files. Find Any File can help in removing leftover components of apps that have been deleted.  Do the following:  

#1 - boot into Safe Mode according to Start up your Mac in safe mode - Apple Support. 

NOTE: Safe Mode boot can take 2 -3 minutes as it's doing the following:• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

#2 - download and run the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  For XXXX software you'd do the following search(es): 

1 - Name contains XXXX

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

#3 - reboot normally.

hi

Reinstall the drivers, or talk to provider for updates... accessories are an old and notorious fail point when sys updates happen... all the way back to System7 &co...

Good luck

d