It seems as if the use of breakpoints in syntax files could be useful, but so far, I haven't been able to make it work. Addition of breakpoints, the red dots in the window margin is easy, but there are no arrows for blocks of code. Any suggestions?

Hi @Robert Lundqvist
This issue is being addressed as  Known Issue DT378592.  IBM SPSS Statistics 30.0.0.0 (172) fixes the underlying behavior, but it can look like it is not fixed based on other settings you have under "Edit -> Options".  Please see Known Issue DT378592 and the published workarounds.