I have recently traded in my D850 with some Nikon lenses for the Sony a7iv after a lot of soul searching having used Nikon for over 50 years. I enjoy wild life, basically Africa. Reasons for change over were weight of equipment , looking for improved function such as eye autofocus, animal bird human, ether auto tracking and focussing. I have had a lot of time to devote to using the camera and the learning curve is quite steep,more than I thought. In summary I am impressed with image quality, lenses are great amd mid range lenses not that expensive. Very happy with changeover and hav not touched my remaining D500 since..
The a7iv is a very different camera to the a7Riv and do not mix the 2 up. Suggest you rent one for a few weeks and try it out. For info on how to use Sony manual sucks so go to MarkGaler‘s website. The video is good and changing over from still to video easy