The right column of the plot_trace is a line plot of the posterior. The name plot_posterior is a bit confusing, especially given how it can be used for other groups too. The left column of plot_trace is a kde or histogram of the posterior, the same type of plot as plot_posterior or plot_density but each has its own particular style. I think I understood the question after reading the previous discussion but wanted to clarify that I am plotting the posterior, even if using a different type of visualization than plot_posterior
I believe a variation of the code below adapted to your case will achieve what you want
import arviz as az
import matplotlib.pyplot as plt
idata = az.load_arviz_data("rugby")
idata.posterior.atts.plot(x="draw", hue="chain", col="team", col_wrap=3)
plt.show()
InferenceData is not 100% custom made like MultiTrace so it builds on top of all the amazing work done by the xarray team. We can therefore use it’s methods to plot like we did here but also to summarize quantities, perform post-processing… everything using named dimensions, which is something I personally love because otherwise I mess up the dimension order, or come back to the code and don’t remember anymore if axis=2 meant reducing the subject or the experiment dimension.