I have a similar system, but I'm running on a custom kernel from the 4.19 branch: `4.19.38-custom` to be exact and these keys do not produce any output under `xev`, `xinput`, nor even `showkey` on a console.
*However,* `acpi_listen` does show the keys are active, just that the kernel doesn't convert them to keypresses, so I tried with the following kernels:
* `5.0.21`: The latest build of the 5.0 series
* `5.1.15`: The latest build of the 5.1 series