Yes, fullresolution=1920x1080 solves the problem. However, in this case I have the box in the center of the screen where there is an image. There is no 1920x1080 image in full screen mode.
I have Dosbox v0.74-3 running on Linux, Ubuntu 20.04.4. When I quit full-screen mode (Alt+Enter) the screen resolution has not been restored to 1920x1080. I need to close the Gnome session and login Ubuntu again to restore the screen resolution. How can I solve this problem?