is there the possibility that the app contains an addon in which you can create own blocks and modules?
I find it unnecessary to use an external program.
you can create things in a 1x1 area inside the application. Then export it as obj, to then put in the folder to use over and over
Could you upload the file somewhere so I can check myself? A few pointers; it needs to be an OBJ file and only works if it contains no hierarchy, all mesh data needs to be in the root.
It seems like your object is too large, the box in the center there is a 1 x 1 x 1 meter box and your model is way larger.