When working with frame averaging, self timer can work, but the issue is disturbing the camera in any way, so pressing the actual shutter release is undesirable.
For frame averaging, a remote release is preferred, because all shots can be made without any physical contact with the camera, thus eliminating that potential source of error.
Remote release for Sony mirrorless
This is super easy—wireless is built in and the remote is reasonably priced and its weight and size are OK too.
Remote release for Nikon DSLR and Nikon Z7
Choosing the appropriate remote release for some Nikon cameras can can be frustrating, starting with ambiguous descriptions like “for select Nikon cameras”.
With Nikon, it gets messy for wireless solutions, all having annoying two-part remotes for some cameras that require use of the hot shoe for a receiver—fine for a studio but crappy for field work, adding bulk and weight.
There are also wired solutions which vary by camera model. This approach carries some risk, since there is a wire connecting the remote to the camera, which could cause micron-level disturbances by the user or just by wind. So it requires care. I use the Nikon MC-36A with the Nikon D850 but always have this concern of using a wired remote.
For wireless and with extra bulk and nuisance, there are numerous solutions. The Vello RS-N1II Wired Remote Switch is cheap and smaller and I should probably get one). I am annoyed at having to plug it into the camera both for the hassle and the risk of affecting the camera slightly from the protruding wire—it’s a lousy solution for hiking and similar where the wire can get caught, and stow/unstow are harder/bulkier. The Vello Free Wave Plus Wireless Remote Shutter Release looks smaller and better.
Remote release does not solve it all with Nikon...
Remote or not, the Nikon D850 is brain-dead for multiple exposures: it requires the second curtain shutter for all bracketing or self timer modes with bracketing (I am unsure if the Nikon Z7 offers a better alternative). The issue is the shutter bang-bang-bang-... bang—so some shutter delay between frames is needed. You might get away with it much of the time, but you cannot count on vibration-free results and that means it is a non-starter for good shot discipline.
One serious problem can be that a delay of a second or longer between frames can be the kiss of death if external conditions vibrate the camera or move the subject—a half pixel or even quarter pixel movements are not OK. Plus, if there is wind, a strobe effect is ugly and there is also a strong risk of tiny vibrations in the tripod and thus the camera, so even if the shutter speed is high, individual frames might wiggle around so as to not align perfectly, which will slightly blur things.
The best way to do it but one that does not allow for in-camera averaging is to use silent shutter (full electronic) and bang out the exposures at 6 fps—no vibration, and far lower chance of subject movement or lighting changes. A full electronic shutter has its own downsides, namely subject movement and the jello effect. But if the subject matter is moving, the strobe effect is worse problem.