For those interested in my reports about our Nikon Z8 & Z600mm f/6.3 PF AF issues, with and w/o Nikon's native 1.4x Z TC, a brief update. We AFMAd both combos with my old Spyder Lenscal, distance 10 m (typical setting for shooting smaller birds). Without TC it showed a massive backfocus, with TC on it was even worse. The Z8 allows to save different AF microadjustment settings for the combo with and w/o TC, fortunately. Our first days out for birding after that procedure showed a substantial improvement in AF performance for both combos, in fact the combo with TC was the first time really useable without residing to manual focusing. Only real action with birds in flight is not yet tested due to the lack of occasions.
So it really makes sense that Nikon still offers the option in their Z camera menus to AFMA lenses (at least in their pro/prosumer cameras). Canon, by contrast, obviously relies much more on auto correction algorithms "under the hood" with the RF system. So far, I have no complaints, as a Canon user I am happy that I don't have to bother anymore with AMFAing all my "AF critical" lenses, what always required quite a bit of work.