At a first glance, (g) might seem non-stationary but these cycles are aperiodic, and is dependedent on the complex interactions between lynx population and the availability of the food source. The timing of these cycles is unpredictable hence, this time series is non-stationary.
The time series is stationary because of those reasons.
There is some content here that is copied from https://otexts.com/fpp2/stationarity.html. On top of this, there are typos and errors in the text, for example
The time series is stationary because of those reasons.