What is a good way to make an app ..., to open in the same place and size every time it starts?
In KDE I propose that method :
open the app
give the window the size and the position you want on the screen
right-click the title bar of the window and choose Advanced/Special Window Settings...
enter the Geometry tab
check Position and choose Apply Initially
check Size and choose Apply Initially
click the OK button.
That should open the app at the same place and with the same size the next time you open it.
I use that and it works for me like that.