This alone does not fix the issue in my case.
Wouldn't it make sense to keep the popup menu open, until it is left with pointer or focus?
Currently it seems to be expected that the popup always hides when a selection is done, but probably one wants to go on selecting or de-selecting other graphs, or even one just wants to see the effect (tick/un-tick) in the metrics list?
@MichaIng did you clear the matomo cache & browser cache when testing?
Ah sorry, thought about browser cache and OPcache but forgot Matomo cache. All fine now, working nicely. I still think it would be good if the dropdown would stay open but I'll open a new issue for this.