Auto-Reflow on Mac OS

I have build an 3-panel app with Auto-Reflow in MATLAB R2019b App Designer for Mac . But it seems not to work since the size of the window is the same as without Auto-Reflow, just way to small. Are there any problems with the Mac OS version of MATLAB known already? I was expecting the window to fill the screen with Auto-Reflow. The property for the size in the sidebar is gayed out. So I am not able to set a bigger size from the beginning. If I set a biger size on startup function all elements in the app stay small though they are resizing if I drag the window bigger. There must be a simpler methode than to manually resize them all...