The Object Storage Repository is different than other repositories and requires different PowerShell commands.
Get-VBRObjectStorageRepository is the PowerShell command for this type of repository that provides good information, but it does not provide the value for Limit Concurrent Tasks that is available in the GUI shown below.
I used [Veeam.Backup.Core.CBackupRepository] to get the used capacity for this type of repository. Can this be used to get the max concurrent tasks?
It doesn't look like there's a supported way (though Oleg can correct me if I'm wrong), but you can use this unsupported method below. Note that this may change in future releases, and no support is offered for using this method:
It is, indeed, not supported yet as of v11a. So, the only way to get tasks count is the one David showed.
Good news though - in v12 we are planning to add MaxTaskCount property to VBRObjectStorageRepository class.