Create object and update manytomany field at the same time

Hi, I’m trying to refactor a FBV to a CBV. The view is similar to updating a comment on a blog, but I also need to be able to update a many to many field at the same time, which is just a checkbox. I’ve managed to get it into a CBV but without the checkbox. I’m assuming that Createview is not practical as I’m accessing two models at once. How is this addressed in django? here is what I have so far using a CreateView at the moment, Please excuse the naming, it’s a little confusing but “update” refers to giving an update to a project in a meeting, it’s not a django reference:

class UpdateView(CreateView):
    model = Update
    form_class = ProjectUpdateForm
    template_name = 'project_portal/project_update.html'
    success_url = reverse_lazy('project-update')
   
    def get_context_data(self, **kwargs):
        context = super().get_context_data(**kwargs)
        context['project'] = Project.objects.get(slug=self.kwargs['slug'])
        return context
 
    def form_valid(self, form):
        project = Project.objects.get(slug=self.kwargs['slug'])
        form.instance.project_id = project.id
        return super(UpdateView, self).form_valid(form)

And Here is the form I am using, the task complete is what I need to be able to update:

class ProjectUpdateForm(forms.ModelForm):
    """
    Form used for adding Updates to Projects.
    """
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.helper = FormHelper()
        self.helper.form_method = 'POST'
        self.helper.add_input(
            Submit(
                'Update',
                'Update',
                css_class='btn-primary'
            )
        )
 
    task_complete = forms.BooleanField(initial=False, required=False, label='Task Complete')
 
    class Meta:
        model = Update
        fields = [
            'category',
            'update',
        ]

What is the best way to do this?