On this page says that Redmine 4.0 cannot support sql server:
Microsoft SQL Server 2012 or higher
Redmine 4.0 does not support SQL Server as of December 2018 because a dependent library activerecord-sqlserver-adapter does not support Rails 5.2 yet.
According to this thread now we a have a release candidate for active record with support for rails 5.2.
Have a look at this release
Perhaps somebody could start giving it a try.
Thanks for the release, I'll try to test it this weekend.
Don't thank me, I'm just bringing the good news ;-)
It would be great that you could give it a try, thanks!