Gotcha, I'm preaching to the converted here.
I think on my 50ii the high is at 8000 maybe 6500, somewhere in there.
I will do some research/ testing before fully deciding. 800 as my comfort zone goes way back. I need to adjust to the modern times.
I've kept my Z30 and returned the Z50II because after using it for three days, my thumb was not able to get the BBf button, and when I used the shutter with the thumb-point, it made a bleeding sore on the middle of the thumb skin. [My hand is 13cm large and my fingers are under 8cm short

].
Alas, they made that button buldging too much.
Back to ISO.
Z30 and Z50II have the same sensor.
My Auto-ISO is set in the 100-6400 during the day and 100-10/20.000 at night.
I shoot in M and, depending on subject/light, I decide what speed I need or what DOF/grain I want. I keep a tab on the ISO to keep it at camera best: 100 or 400 when possible. Not very often, I do switch to manual when I have a strange unexpected readings. Usually, these are due to a Lamp, a Window in the interior. Outside, Direct sunlight, or a Reflection.
Otherwise, I don't care to shoot 6400ISO or 20.000, provided the speed and DOF are what I want.
Around your shot in the digital world, there is a lot of software: camera software, PP, Denoising, whatever you need is there.
Note: Z50II has better software and image management than the Z30.
ISO is not the important issue as it was in the film era, when you were forced to respect 64ISO or 200ISO.
I'm printing a 2mt poster from a Z30 shot. 1/320; f/14; ISO 900
> In the same way, I use the Zf
( Auto-ISO unlimited is a benefit to be used, not to be shunned )
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