Sorry, but I cannot find any current Apple articles with the details since it appears Apple has removed any easy to find references to the preferred file system for a TM backup drive. I believe beginning with Big Sur macOS now prefers to have TM drives formatted as GUID partition and APFS (top option). Here is the general product page which also includes access to the Samsung proprietary software: Here is a link to the Samsung T5 SSD user's guide: I've encountered some scenarios where the first attempt to erase a drive will fail, but the second attempt will succeed. If you still get an error, then immediately try to erase the whole physical drive again. Select the physical drive and erase it as you described: GUID partition and MacOS Extended (Journaled).
Within Disk Utility click "View" and select "Show All Devices" so that the physical drives appear on the left pane of Disk Utility. If the external drive supports hardware encryption, that is a nice feature, but relying on a proprietary app to control it is risky. If you want the drive to be encrypted, then you can have macOS encrypt the drive or you can use VeraCrypt a third party app with cross-platform support.
#Samsung ssd format utility software
Then uninstall the Samsung software by following the developer's instructions.
It is best to have the Samsung software reset the drive's settings to default and to disable encryption if encryption is currently enabled. Make sure the Samsung software does not have a lock on the drive and if the drive is encrypted, then make sure the drive encryption is unlocked before you attempt to erase the drive. If you are using the Samsung proprietary software to manage the drive, then perhaps that software is either locking the drive or it is encrypting the drive.