Why do you think Red Bull wouldn't back it, I can't see how it would affect them in a negative way..Apparently they need six teams to back it: Williams, Sauber, Alpine and Haas are surely all going to back it. Alpha Tauri should back it, but they're Red Bull puppets so they won't back it unless Red Bull do, and I think Red Bull are one of the least likely teams to back it.
So I guess we need two out of Merc, McLaren, Aston, and Ferrari to back it. Merc probably will, since they tend to be willing to do stuff to help the smaller teams and they have a good relationship with Williams. Ferrari probably won't, I think, and I really have no idea which way McLaren will fall. Aston should realise that it will benefit Stroll.
Also Autosport are saying only five teams are required https://www.autosport.com/f1/news/f...s-on-course-to-get-support-it-needs/10602004/