A drive with no letter or a drive letter that is different from the one in the network mapping in Windows Disk Management are two other possible causes of this problem.

Learn how to recover Deleted Files or Folders from a Network drive on your computer.,& how to enable Recycle Bin on Mapped Network Device.

If your Windows 11/10 is not able to load the network drive, then here is how to reduce long timeout on a Network drive in Windows computers.

Based on your reply, I'm assuming that Microsoft Backup software (bundled with Windows 10/11) doesn't have the ability to backup to a mapped network drive similar to what you described with Veeam?