How can I plot a simple 3D region such as
If I can't do that directly, how can I turn it into
$$x=\dots$$ $$y=\dots$$ $$z=\dots$$
So I can use Mesh --> Math Function --> XYZ Surface?
Or is there a script that can plot
by brute-forcing for each $x$, $y$, and $z$ values of step size $d$ then plotting that?