The Sony Alpha A7III can track humans and animals.The A6700 is more advanced. It can track humans, animals, birds, insects, cars, trains and airplanes.
The Sony A7III supports a maximum shutter speed of 1/8000 sec.The A6700 also supports a shutter speed of 1/8000 but only when using its electronic shutter.
The Sony A7III features IBIS with 5.5 steps of correction.The A6700 also has IBIS but with 5 steps of correction. It also features Active Movie stabilization.
The Sony A7III display is limited to tilting up by 107 degrees and down by 41.The A6700 features a much more versatile vari-angle display with a slightly higher resolution.