Shows I need to do some research first before posting
Just watched a few videos, unfortunately couldn't find a comparison between the Z8 and A7RIV but the Z8 seems to be behind the A7RV, being plagued by the same issues that have plagued Nikon for as long as I can remember in that it will sometimes focus on the foreground or background rather than the subject. Of course, we're nit picking here but this is how far we've come with AF systems now.
The Z6III video I watched was worrying. Admittedly it was by the Nrothrups but in a test of Chelsea running towards the camera the A7 IV got 92% in focus, but the Z6III a pretty poor 64%, also missing several shots in a row.
If it was me and I wanted to try something different and was worried about AF I'd go with Canon, they appear to have leap frogged Sony with a lot of their cameras barring maybe the A9 III and A1 II.