David Martin wrote:
Blackrapid sling which comes in both right- and left-handed versions. Allows your shoulder to bear the weight, with the camera hanging upside down at your side. I've used mine with Nikon D500 + 200-500mm lens, and with Canon R5 + 100-500mm lens, with the strap attached to the tripod mount of the lens. With a smaller/lighter lens, attach the strap to the camera.
I use the same approach for my Nikon D850 with 200-500 zoom. But I can't just let the rig dangle from my shoulder when moving, so the strap takes about 50% of the weight, and my grip on the tripod mount carries the other 50% and keeps it all steady. This is a very low-tech approach to the issue. You can get way more complicated and spend a lot less money for not nearly as good results as this.