On the EOS 1200D, the magnifying frame in Live View is part of the camera’s focusing/magnification display and generally can’t be fully disabled. For astrophotography, a practical workaround is to use manual focus and move the magnified area onto a bright star, then use the zoomed Live View image to fine-tune focus. Lowering screen brightness, if available, may also help reduce distraction. If the frame is preventing you from seeing faint stars, try first aiming at a brighter star or distant light to set focus, then recompose.