Hi,
Indirect upgrade paths to SCOM 2019:
SCOM 2012 R2 -> SCOM 2016 -> SCOM 2019
SCOM 2012 R2 -> SCOM 1801 -> SCOM 2019
Upgrading to SCOM 2019 Step-By-Step
We could use SCCM package deploy the command line:
To deploy the Operations Manager agent with the command line
https://learn.microsoft.com/en-us/system-center/scom/manage-deploy-windows-agent-manually?view=sc-om-2019#to-deploy-the-operations-manager-agent-from-the-command-line