I am trying to change the DPI of QGIS3 (3.6) in the layout manager. However, as the Figure below shows (lower left corner), the DPI (300 by default) seems to be read only.
I tried to click the textbox. But it's not allowing input. There is no spinner control QGIS 2 either as said about the the older QGIS2 in GIS.SE:
How can change the DPI from the QGIS 3 GUI?