django admin show field only if checkbox is false

How about overriding get_form method on a ModelAdmin, like this:

class MenuModelAdmin(admin.ModelAdmin):
    def get_form(self, request, obj=None, **kwargs):
        self.exclude = []
        if obj and obj.has_submenu:
            self.exclude.append('page')
        return super(MenuModelAdmin, self).get_form(request, obj, **kwargs)

Also, please, see get_form docs.

You can use jQuery within the Django admin:

class MenuAdmin(admin.ModelAdmin):
    # ...
    class Media:
        js = ('/static/admin/js/hide_attribute.js',)

ModelAdmin and InlineModelAdmin have a media property that returns a list of Media objects which store paths to the JavaScript files for the forms and/or formsets.

Contents of hide_attribute.js:

hide_page=false;
django.jQuery(document).ready(function(){
    if (django.jQuery('#id_has_submenu').is(':checked')) {
        django.jQuery(".page").hide();
        hide_page=true;
    } else {
        django.jQuery(".page").show();
        hide_page=false;
    }
    django.jQuery("#id_has_submenu").click(function(){
        hide_page=!hide_page;
        if (hide_page) {
            django.jQuery(".page").hide();
        } else {
            django.jQuery(".page").show();
        }
    })
})

Namespacing:

To avoid conflicts with user-supplied scripts or libraries, Django’s jQuery (version 3.3.1) is namespaced as django.jQuery.