I spent a few hours last week to test the GP2018, web client and Management Reporter 2012 CU16 compatibility with SQL Server 2017 on Windows Server 2019, there is no problem for GP2018 and web client as I tested, the only problem that I see was MR2012 having issue to create Application and Processing services while you are going to create a new Management Reporter database on SQL server 2017, the workaround is to get a copy from the other SQL server and restored it on SQL server 2017 then you can run Dynamics Configure utility from MR2012 to create Application and Processing services, you can select Data Mart or Legacy connection method after that, run MR2012 SQL moving script, you can login to MR2012 without any problem.