Considering this is a 10 years old android tablet that cost at the time ~300$. I probably could have bought directly a more modern one which is known to be flashable with linux.
The sentence I cited resonate for me as I often dive in a project and follow in the rabbit holes even though I know it's a bit irrational to do it.
About how to do it: - you first have to find every git repo that may have relevant patches for this or similar device. There's the one open-sourced from the manufacturer, Google has one dedicated to the Tegra chipset, with more recent stuff but without any specifics about that device. - determine what parts are relevant: definitely the board definition, the drivers. But then, that file weirdly named which appears to handle interrupts? Well better take it. - adapt to changes in kernel interfaces: I've only come across name changes for now, but you can imagine it gets more complex - finally: compile, flash, test! And probably keep doing that for a few cycles.