The AD FS upgrade scenario from 2012 R2 to 2016 with a SQL database is missing 2019 info
The following link contains the steps to upgrade an AD FS farm from 2012 R2 to 2016 when a SQL server is involved. It does not mention 2019.
Is it possible to add it? The process is similar the only difference is the FBL.
The link to the article: https://docs.microsoft.com/en-us/windows-server/identity/ad-fs/deployment/upgrading-to-ad-fs-in-windows-server-sql