Is MS SQL Server 2017 Supported as Data source?

If it isn't in the release documentation it isn't supported. It will probably still work in the case of SQL Server, but Appian hasn't completed their internal QA process to officially support it. The best thing to do is to inform Appian that your organization is looking into using it through a support case (including timelines for when you are looking to implement the new version of the database). This helps Appian's engineering team to better understand customer needs and prioritize adding support for newer database versions.

If it isn't in the release documentation it isn't supported. It will probably still work in the case of SQL Server, but Appian hasn't completed their internal QA process to officially support it. The best thing to do is to inform Appian that your organization is looking into using it through a support case (including timelines for when you are looking to implement the new version of the database). This helps Appian's engineering team to better understand customer needs and prioritize adding support for newer database versions.

Thanks Eric and Phil. we are going to try two things in parallel - try adding mssql 2017 as data source on an internal environment and see if it works, And raise a ticket with the APPIAN support.

How will you really know if it works? There are so many potential edge cases where it could fail. I would stick with supported versions, unless this is for some internal non-critical application.