Avamar Exchange database restore failing with "The term 'Set-Mailboxdatabase' is not recognized as the name of a cmdlet"

Exchange database restore may fail with errors similar to the following:
 

2021-03-26 10:52:00 avexvss Error <0000>: The term 'Set-Mailboxdatabase' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
2021-03-26 10:52:00 avexvss Error <0000>:    at System.Management.Automation.Runspaces.PipelineBase.Invoke(IEnumerable input)
   at ps_calls.invoke_command(Pipeline pipeline, Command ps_command)
   at ps_calls.set_mdb_allow_file_restore(String msg_parms)
2021-03-26 10:52:00 avexvss Error <13225>: Unable to continue with restore -- code 0x80004005: Unspecified error.
2021-03-26 10:52:00 avexvss Error <13226>: Possible RDB/RSG creation latency issue.
2021-03-26 10:52:00 avexvss Info <8394>: Deleting temporary stored metadata files...
2021-03-26 10:52:00 avexvss Warning <13028>: File C:\Program Files\avs\var\avexvss_restore\{76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}0.xml cannot be removed. Error code 2
2021-03-26 10:52:00 avexvss Warning <13028>: File C:\Program Files\avs\var\avexvss_restore\{76fe1ac4-15f7-4bcd-987e-8e1acb462fb7}0.xml cannot be removed. Error code 2
2021-03-26 10:52:00 avexvss Error <12995>: Restore failed -- code 0x80004005: Unspecified error.

The "Backup Agent and "DELL Avamar for Exchange GLR" services are configured to run with local SYSTEM accounts. This account does not have sufficient permissions to run PowerShell commands.

This may occur when the Avamar plugins are reinstalled or upgraded, as it defaults to the local SYSTEM account.

Open the services.msc console and reconfigure the avagent and GLR services to run with the "avamarbackupuser" and similar account with the required permissions.

In most environments, you can use the Avamar Exchange Backup User Configuration Tool to automatically create the account with the required permissions and configure Avamar services.

It can also be created manually. Follow the steps under the "Creating and configuring the account with the Avamar Exchange Backup User Configuration Tool" section of the DELL Avamar for Exchange guide.