Backup to unc path in workgroup environment I am having a problem backing up the database to the network path using dbatools.io Backup-DBAdatabase command.
This is a workgroup environment. The SQL Server runs under the NT Service\MSSQLSERVER account. The location I am trying to backup is a standalone  NAS drive.
I mapped the network folder to the SQL Server machine but when I backup to that drive it fails with

WARNING: [14:25:08][Backup-DbaDatabase] Backup Failed |
System.Data.SqlClient.SqlError: Cannot open backup device
'K:\BackupTest\15Jan2021_12_34\full\sdsd_180_infras_b18c6_202101151425.bak'.
Operating system error 3(The system cannot find the path specified.).

If I use the UNC path I get

WARNING: [14:24:04][Backup-DbaDatabase] Backup Failed |
System.Data.SqlClient.SqlError: Cannot open backup device
'\\XX.XX.XX.XX\backup\BackupTest\15Jan2021_12_34\full\XX_180_infras_b18c6_202101151424.bak'.
Operating system error 1326(The user name or password is incorrect.).

I am aware the issue is due to the SQL Service account's lack of permission on the NAS folder not sure how can resolve it.
I really appreciate your help
the problem are not coming from the dba tools but from your network.
You can't mount a share on a local path. That path (K) can't be seen by sql server.
The unc path works with the user that is running the sql server service, in your case the computer account; but you can't authorise the compunter account in your nas under workgroup.
The only option i can suggest you to test is to change the sql server user to a local windows user and then create a user in the nas that match it in the username and password.
Then you can try with the UNC path; but i'm not sure if it will work.