Bought a new Lenovo Tablet M8 HD. I want to completely replace the Android O/S, where to start?
You have to search if anyone has ported Linux to that device already.
I am pretty sure that it is currently not supported by Manjaro, but that does not mean no one else has done it.
If there is no distro already and you feel adventurous you can check if the SoC (Processor) is supported by Linux and try to build it yourself. That not that easy though and needs a lot of trial and error.