External Hard Drive( Seagate Back Up Plus ) not mounted

Kamathampalli wrote:

We are not sure, is that Mac not able to Mount the drive ( earlier version has smooth recoginistion ) or Seagate drivers should be updated along with newer version of Mac

does that mean you are currently using seagate's preloaded software on the drive that is supposed to make it "mac ready"? if yes, that could be the cause of your issue. 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 seagate 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 the seagate device before putting it back into service. or if you have another mac running the macOS that the drive was working on, you can use that mac for the same purpose.

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

File system formats available in Disk Utility on Mac - Apple Support

When I have irksome drives, I format on Windows to NTFS and that has always made the drive useable again on a Mac. I don't recall a single instance of that not working.

I do sometimes use a GPartEd (Gnome Partition Editor) live CD with our Windows box and that works too. With GPartEd you can directly format to Apple if you wish. I prefer the NTFS route to "clear everything away" from an Apple standpoint.

External Drives do get corrupted and usually because the drive was not properly uncounted when in use and or because it is in a state of failing.

If the data is not replaceable and the user MUST preserve the data, suggest STOP using it period.

search for a Professional Reputable Data Recovery Company and get an estimate for them to Recovery some of the data.

it will cost a good amount of money and not ALL data will be salvaged

If this External Drive was used for a Time Machine Backup on previous versions of macOS and now under Monterey ?

User wrote " The external drive Master Boot Record of Seagate volume also fine "

This implies the Drive was and is formatted in a Microsoft Drive format.

MBR format is a very fragile drive format and is easily corrupted.

In that case and the Data Must be salvaged - the Professional Data Recovery Company may be required.

In the supplied picture above you are running Repair on the Volume that is on the drive.

Suggest running the same Repair on the Drive, In your picture, the drive by Name