Disk was not ejected properly

Many have reported this issue with Monterey. The only issue when it is ejected is if you were moving files to this disk at the time then it may not have completed the operation. I do not believe it will harm the drive. I have had this issue many times and the drive is still OK.

Hmm.. if you have tested a different port and cable, then the problem may be a by-product of the exFAT format.

If you are using the drive to share files between a Mac and PC, then using the exFAT format is a must.

If you are using the external drive strictly for Mac file storage and backup, then Mac OS Extended (Journaled) or APFS is the preferred format to use. see > https://www.hellotech.com/guide/for/how-to-format-a-hard-drive-for-mac

Problem you have now is, that re-formatting an external drive erase's all of the current data on it and you will need to copy the current data to another drive, then copy that data back after reformatting the external drive.

Last question, when do you most often get the “Not ejected properly” message?

(randomly, after sleep/wake, startup, other)

Test it on a different Thunderbolt 4/USB-C port.

Test a different Thunderbolt 4/USB- C cable.

Uncheck “Wake”, should fix (restart after making change).

What iMac model?

https://support.apple.com/en-us/HT201634

What external drive?

(make & model)

What is the external drive used for?

(Time Machine or something else)

How is the external drive connected to the iMac?

(USB-A, USB-C, thru a Hub or Dock)

Sorry for all the questions, but they are necessary in order to help you troubleshoot the problem.

Could you post a snapshot of your Energy Saver Preferences please?

Please upload it here. Select the icon to the left of play button on the message options bottom panel to upload.