Is there a way to configure CSI to use VS 2019 as default script editor/debugger?
You can associate any type of file (eg. JS) to VS2019.
in Syteline 9, on the User Prefs screen, is there a way to configure a more recent version than VS 2010 VS express as default debugger? See screenshot below.
The short answer is no, there is no way to do that.
Not much help to you, but they have added VS 2019 for CSI 10.