Smoothing feature: original curve does not become transparent

As per title, the smoothing feature is not working properly in all plots of all my projects, i.e., the original curve does not become transparent when I turn on smoothing. See also the image above.

Following the recommendation in this (old) thread Semi-transparent smoothing stopped working I can manually edit each plot and toggle the “Show original” option, but there is no global way to do this for all the plots. How can I fix this?

Thank you for your help!