External hard drive won't mount after power blip

After a momentary power interruption this morning, my external hard drive (on which I have a Time Machine backup) does not mount and does not appear in Finder. (It is a LaCie 2TB USB drive.) The device is recognized in System Information and Disk Utility, but an attempt to mount it in Disk Utility returns this error message:

Could not mount “disk2s2”. (com.apple.DiskManagement.disenter error -119930868.)

I have tried First Aid in Disk Utility but it fails. Restarting the computer did not help either.

I have a Mac Mini (Late 2014) running MacOS Big Sur Ver. 11.6.2.

Any suggestions would be appreciated. Thank you!