Let's find the inflection points, we'll need to solve the equation for this
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
the second derivative$$- \frac{4 \left(6 \delta\left(\frac{2 x - 1}{3}\right) + \frac{\left(2 x - 1\right) \operatorname{sign}{\left(2 x - 1 \right)}}{1 - \frac{\left(2 x - 1\right)^{2}}{9}}\right)}{27 \sqrt{1 - \frac{\left(2 x - 1\right)^{2}}{9}}} = 0$$
Solve this equationSolutions are not found,
maybe, the function has no inflections