--- EDITED ---

n_osversion.of_pbvmname(), used by the code waaay below, will return "pbvm190.dll" for ALL different versions of powerbuilder 2019. I've adapted it in the hope it will now also return the correct name for pb2019 R3, R2 and R1.
So my best advice for now, is that IF you are using the R3 release of PB2019, use these 2 lines of code in n_cst_platform constructor event and nothing else.

// pb2019 R3
is_ClassName[1] = "FNWND3" // mdi window
is_ClassName[2] = "FNWNS3" // response window

I've modified the code of my n_osversion object to also check the minorRevision for pb2019 r3 (which is 2). I'm not sure yet if a value of 0 would represent R1 and a value of 1 would mean R2, but the same thing happened with pb2017. (see: https://www.appeon.com/standardsupport/search/view?id=1984 ).
I've attached the exported code of n_osversion.

// This function the name of the PowerBuilder VM file.

Environment le_env
String ls_vmname
Integer li_major

GetEnvironment(le_env)

li_major = le_env.PBMajorRevision
choose case li_major
	case 10, 11, 12, 17
		choose case le_env.PBMinorRevision
			case 5
				ls_vmname = "pbvm" + String(li_major) + "5.dll"
			case 6
				ls_vmname = "pbvm" + String(li_major) + "6.dll"
			case else
				ls_vmname = "pbvm" + String(li_major) + "0.dll"
		end choose
	case 19
		if le_env.PBMinorRevision > 1 then
			ls_vmname = "pbvm.dll" // pb2019 R3 or higher, R3 has a minorRevision = 2
		else 
			ls_vmname = "pbvm190.dll" // pb2019 R1 or R2
		end if
	case else
		ls_vmname = "pbvm.dll"
end choose

Return ls_vmname

--- End of EDIT ----

Hi all,

Now with the recently released R3 version of pb 2019 here's some code:

If you use PFC classes make sure that your n_cst_platform object has the correct values for the is_ClassName[] variable.
I'm not completely sure what the is_ClassName is used for internally, but it helps to have to correct values assigned to it.

So this is what I do in the constructor event of n_cst_platform (for the different versions of powerbuilder that we use, 12.6, 2017 and 2019 R2 and R3):

// get the version of POWERBUILDER:
n_osversion ln_osver
string ls_PBVMName

ls_PBVMName = lower(ln_osver.of_PBVMName())
choose case ls_PBVMName
	case "pbvm.dll"  // pb2019 R3 (and maybe later versions too?)
		is_ClassName[1] = "FNWND3" // mdi window
		is_ClassName[2] = "FNWNS3" // response window
	case "pbvm170.dll" // pb2017
		is_ClassName[1] = "FNWND3170" // mdi window
		is_ClassName[2] = "FNWNS3170" // response window
		is_ClassName[3] = "AfxMDIFrame100su" // pb2017 for "dockable MDI" 
	case "pbvm190.dll"  // pb2019 R1 / R2
		is_ClassName[1] = "FNWND3190" // mdi window
		is_ClassName[2] = "FNWNS3190" // response window
		// v2, mjl, 06/04/20: dockable MDI is now obsolete in pb2019 R2, commented:
		//	is_ClassName[3] = "AfxMDIFrame100su" // pb2019 for "dockable MDI", same as PB2017
	case "pbvm126" // pb 12.6
		is_ClassName[1] = "FNWND3126" // mdi window
		is_ClassName[2] = "FNWNS3126" // response window
end choose

Regards