Send-SmigServerData etc seems to be deprecated for later OSes - these are Server 2012 (and earlier) commands. As it stated, the recommendation is to use the Storage Migration Service, which can move SMB data, local users and groups, and some server configurations.
However, since you're moving between Server Essentials versions, these are domain controllers, so there are no "local" users and groups. So you should join the new machine to the same domain, then follow any steps needed to ensure it's promoted as a domain controller and replicating users (sorry, I haven't worked with Server Essentials for many years, so am not sure of the precise steps now). Then you can use Storage Migration Service to migrate file data. As noted in the link above, you can't "cut over" DCs using the service. You must transfer the FSMO roles to the new server before decommissioning the old one.
I'd recommend taking a backup/snapshot of the 2019 server and experimenting with how it'd work using a virtual environment.
This is still the most current migration guide (despite references to old OSes) - for the data move step, you can use the newer Storage Migration Service.
And you might find the comments on this question are helpful for summary information - although I'd say moving FSMOs isn't "optional" (it can be done before or after moving the data, though).