thanks. So it's more a question of where tu put the workbench directories than an Asm4 problem first. May I ask you to try the following:
1) when you put the Mod_Asm4 directory in #1 (D:/Applications/FreeCAD/FreeCAD-asm3_v0.10.2/Mod) only, does the Asssembly 4 workbench show in FC19-asm3 ?
2) when you put the Mod_Asm4 directory in both locations (D:/Applications/FreeCAD/FreeCAD-asm3_v0.10.2/Mod and C:/Users/zhubert/AppData/Roaming/FreeCAD/Mod) do you see it in FC19-asm3 ?
3) When you see the Assembly4 workbench, did you try to open some of the example files ?