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$$\frac{\left(\frac{\left(1 - \frac{2 e^{x}}{e^{x} - 1}\right) e^{x}}{e^{x} - 1} - 1 + \frac{2 e^{x}}{e^{x} - 1}\right) e^{x}}{e^{x} - 1} = 0$$
Solve this equationSolutions are not found,
maybe, the function has no inflections