I have a Honda Clarity 2018, which comes with an HMU that runs Android Jellybean 4.2.2-42 (on which I have obtained root).
I can't seem to figure out how to take screenshots on the unit, as it lacks soft navigation keys insofar Android is aware of); in actuality, the unit has soft-keys that are directly adjacent and outside of the Android UI boundary (shares the same screen), but they are not treated as the native "on screen navigation keys", yet nor do they follow the same behavior as hard-keys normally would. Additionally, there are actual hardkeys mounted into the steering wheel, which I've utilized a 3rd party utility to successfully bind actions to, but screenshots are not part of the list of actions included by the developer.
Digging around the root directory contents, I recall seeing a .jar package named screenshot or something to that effect, so I'm fairly certain it's available. I also recall coming across somewhere in the config files a list of all possible keyinputs, but these were enumerated in the form of what looked to be scan codes or something of comarable nature, with no further verbose explanations for key functions nor how to bind them to an available trigger.
Considering it's my car, I'd like to see a solution that doesn't involve peripheral devices or ADB through external connection. Unfortunately, unless I figure out how to whitelist the potential custom bindings, the vehicle would likely revert any changes on reboot, but I do have local terminal access so I'm not sure if a .sh script can be utilized to re-apply on boot/manually?
PS: if it matters at all, I use MessageEase IME rather than the default Android keyboard input (which I've disabled).