OP is probably saying that the text editor they’re using doesn’t show when Anki is in full screen, so they want the title bar to disappear to use the maximized window as a workaround.
OP, you can try this addon which I haven’t tested:
https://ankiweb.net/shared/info/2073533957
Alternatively, you can add a <textarea> to your templates as in Add support for typing multiple lines in answers - #4 by eroscard.