Correct me if I'm wrong but I guess that you are using an Angular Material. In that case, the dialog.open function should be called without the this keyword - that's because the dialog.open is available in global scope, not on the this (which points to the point in that case).
Let me know if this solved your problem, and if not - please recreate your issue in an online code editor, so that I can have a proper look into that.
It seems that there is a problem with the Angular Material, please double check that you are importing the Angular Material correctly and setting the default options for the Dialog, but that is only my guess works.
Although we do provide support for the Highcharts Angular wrapper, we have no knowledge about the Material component. In that case, I'd suggest asking on a more general forum i.e Stack Overflow under Angular Material tag.
In case of any other questions related to Highcharts functionality feel free to contact us anytime,
Best regards!
It doesn't look like a Highcharts bug, and as I said before, unfortunately, we do not provide any support for Angular Material - so we can't help with that.
If you are getting undefined, that usually means that you are trying to call a method or property on an object, that does not have this property.