Line PlotOption "Negative values with different color" only working with categories as x-axis?

[FlGraSommer]

I have implemented this new feature into our existing charts application that is using mainly real life measurement values with a timeline. I can't get the different color for below threshold working. After inspecting the examples again and again I realized, that those examples only use categories, not timeseries. Then I adapted the example "Zoomable Timeseries" and added the plotOptions into the options object (well, and changed chart type to "line" and removed the "fill" options) and it is not showing the line in different colors also.
These are the examples I have used:
https://apexcharts.com/javascript-chart-demos/line-charts/negative/
https://apexcharts.com/javascript-chart-demos/line-charts/zoomable-timeseries/