bl_info = {
    "name": "'Display Mode' in Render menu",
    "author": "Sanne, JMcAllister",
    "version": (1, 0),
    "blender": (2, 81, 0),
    "location": "Render",
    "description": "Adds the option to change the 'Render in' user preference from the Render menu.",
    "warning": "",
    "wiki_url": "",
    "category": "Render",
}

import bpy

def render_in(self, context):
    self.layout.separator()
    self.layout.prop_menu_enum(context.preferences.view, "render_display_type", text="Display Mode (\"Render in\")")
    
def register():
    bpy.types.TOPBAR_MT_render.append(render_in)
    
def unregister():
    bpy.types.TOPBAR_MT_render.remove(render_in)
    
if __name__ =='__main__':
    register()