The higher quality YouTube reviews of this camera are spot on. I really liked my A7Rii, but had my eyes on the new A7iii. However, I have recently been wanting to take more images of things that moved rapidly and in all kinds of lighting.
I think I would have been happy with the A7iii, but decided my budget allowed me to go for the A9. I had also decided that 42 megapixels is really not necessary for most things short of high-end product or fashion photography, which I have no interest in. With the high frame rates of modern Sonys, data rates become important.
If you mostly take images of plants and mountains, or perhaps people standing or sitting for a portrait, I would recommend the A7iii. For any kind of action, the A9 is a cheetah. It’s synergistic combination of super-fast and accurate focusing, insane dynamic range, highly-evolved IBIS, and a big, bright, and always-on EVF make action shooting a joy.