The previously leaked MC-N10 Remote Grip option for the Z9 has now been released. It's a close relative to the handle-mounted control systems that have been used on professional video cameras in studios and on platforms at events for decades. Indeed, the MC-N10 adapts the established Arri rosette mounting specifications, which are common in both New York and Hollywood production companies.
In essence, you attach this grip to a fluid tripod head's panning bar and can then control both where the camera is pointed and what it's doing at the same time using one hand. The MC-N10 can also be used on gimbals in the same fashion. The US$430 MC-N10 connects to the camera itself via a USB-C cable, so bring plenty of tie wraps or other cable management, or else you're going to be snagging cables all the time. The MC-N10 requires two AA batteries (for up to 12 hours of use).
In terms of controls, you get a near duplication of the right hand camera grip, including command dials, shutter release, AF-ON button, thumb stick control, and eleven other commonly used buttons, including ISO, Fn1, and Fn2. This allows you to control focus and even review footage conveniently.
While the MC-N10 was mostly intended for video users, still photographers will almost certainly find uses for it, as well. Imagine a camera mounted in a small blind being controlled from further away, for instance.
Update:
You can use the MC-N10 with the Z6 II and Z7 II, as well. One difference between the Z9 and the II models is what you can customize some buttons to. For instance, the Fn1 and Fn2 buttons can be programmed to Hi-Res Zoom (in and out) on a Z9, but not on a Z6 II or Z7 II.
Note that you'll need an Arri Rossette accessory attached to something. A number of such accessories are available on Amazon (not an affiliate link).