A quality 750w will be fine. It's what I am running and I have almost identical specs. (I have more Ram, bigger GPU, more drives etc')
An 850w PSU can *potentially* use more power than a 750w unit (Or vice-versa) as they both have different efficiency curves.
I would choose a quality Corsair 750w PSU over a cheaper lesser-known 1,000w PSU, every single time.
Modern quality PSU's have over-voltage, over-current, under-voltage, short-circuit protection and more, so the risks are minimal/non-existent if you load it with toys.
The RX 6800XT will top out at 300w consumption, the CPU is capped at 142w of power consumption, those two are your biggest power hogs.
He will be fine, it's not his first rodeo in building a PC, even if it only happens once a decade. :P
--::{PC Gaming Master Race}::--
