Maybe look to change your shooting workflow/the way you take pictures if you need to constantly keep 4 buttons pressed in order to capture images.
A lot of people find the capabilities of the newer mirrorless cameras allow them to change the way they used to shoot with older dslr tech.
I have F1 set to quickly change to 3D from my normal Large Wide Area focusing, so back button focus, F1, and the shutter all need to be pressed the same time when taking a shot after switching focus modes on the fly. I'll adapt, for sure, but it's an annoyance.
Oh, this might have a useful alternate method. Something like my Z6 iii setup, but you have more control options on the Z8, I think.
I do 3D handoff or just 3D mode itself with a second "AF-On" button. Here's what I did:
I have AF-On=only, so no half press shutter.
The AF-On button is the currently selected AF mode. It's often on Wide area small or large, or the C1 or C2 custom sized AF boxes (and those are easy to resize without going into the menu.)
I changed the
DISP button=AF-area mode+AF-On. This setting has a
right arrow to select from the list of area modes. I selected
3D-tracking.
I changed the sub-selector center=DISP to switch views (this is the joystick press.) I don't change the view style too often, so this is good. It's not as easy to accurately center press the joystick, compared to reaching the DISP button.
Tracking hand off!
I have Subject Detect turned on.
I hold Af-On, and
when the subject is detected, I can let go, then press the DISP button. This is easy to do by feel. I think I need to press the DISP button within about 1/2 to 1 second to hand off the subject. Now it tracks all over the scene.
EDIT-- I see that the subject tracking sees a subject even before I press AF-On. So if it's already tracking an eye, for example, I just need to press DISP. that's slick.
3D only:
If I just use the DISP button, not the AF-On, it's in 3D tracking mode. It tracks with or without subject detect. Before pressing DISP, I center the desired 3D subject in the center of the AF-On's current AF box. That's usually in the center of the scene, but if I had moved the AF box with the joystick, that's where the 3D box will appear.
Hold the DISP button, and the 3D tracking box appears and starts tracking. Stop holding the button, and the 3D resets for a possible new subject-- good.
I like this
3D only for tracking focus on landscape subjects too. I can track that focus and recompose the scene, and even move around while keeping focus. Nice! Of course, this only works in AF-C. If I'm using AF-S, the DISP button just matches the AF-On focus method.