Here are some video comparisons on Sony a7 III, Sony a7R III and Nikon D850.
Buying options:
Sony a7 III: Adorama, B&H, Amazon
Sony a7R III: Amazon/B&H Photo Video/Adorama/Focus Camera
Sony Alpha Mirrorless Cameras, Compact Cameras & Lenses Rumors
Here are some video comparisons on Sony a7 III, Sony a7R III and Nikon D850.
Buying options:
Sony a7 III: Adorama, B&H, Amazon
Sony a7R III: Amazon/B&H Photo Video/Adorama/Focus Camera