Biztalk in alwayson SQL 2019
Biztalk is compatible with ALWAYS ON from SQL Sever 2016: https://docs.microsoft.com/en-us/biztalk/core/high-availability-using-sql-server-always-on-availability-groups
You have here a brief introduction and a setup of Microsoft Distributed Transaction (MS DTS). Microsoft says that is available starting from SQL Server 2016 Service Pack 2.
I found a link that is talking about best practice and is mentioning Biztalk which is exaclty your scenario but.... it doesn't give any example about how to setup MS DTS with Bitztalk.