iShoot Metal Tripod Mount Ring Lens Collar Compatible with Canon RF 100-400mm f/5.6-8 is USM, Lens Support Holder Bracket Bottom is Arca-Swiss Fit Quick Release Plate Dovetail Groove

FYI & to OP - You can get a 3rd party tripod mount for the RF100-400 from Amazon. I picked up this one (see link) and it works perfect. Highly recommend it if you’re looking for one. https://a.co/d/08xhznia