SharePoint Server 2019 includes a handful of new PowerShell cmdlets They’re fairly self explanatory, but I do want to highlight them as they replace important stsadm functionality.
First is Set-SPApplicationCredentialKey which replaces stsadm -o setapppassword. This would be used in a case where you need to use authenticated outgoing email, another new feature of SharePoint Server 2019, or setting a user to query a domain over a one-way trust. Note that you must run this cmdlet with the same values on all SharePoint servers in the farm. This value is stored in the registry at HKLM\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\16.0\Secure in a REG_BINARY named AppCredentialKey and is not replicated between farm members. There is a corresponding Remove-SPApplicationCredentialKey, as well.
The second is Get-SPContentDatabaseOrphanedData to replace stsadm -o enumallwebs. This only replaces a portion of the stsadm command and as the cmdlet implies, it looks for orphaned data in a content database.
The last set of cmdlets, and probably my favorite, are regarding User Profile Service Application to Site Collection User Information List sync. These replace stsadm -o sync.
Clear-SPContentDatabaseSyncData [-DaysSinceLastProfileSync <Int32>] does the same thing as stsadm -o sync -deleteolddatabases <Int32>. Update-SPProfileSync is a cmdlet that lets you update the UPSA sync jobs between the UPSA and Site Collection UILs. Lastly, Get-SPContentDatabase has a new switch, -DaysSinceLastSync <Int32> that replaces stsadm -o sync -listolddatabases <Int32>. This parameter allows you to see when the UPSA to Site Collection UIL jobs last updated the UIL.