do you want something like this?
I think you need an expression for each type of activity, like
Label = type A, expression =count (if (type='A', type))
Label = type B, expression =count(if (type='B', type))
Then use style subtype "stacked" and in Expressions display options "line" for the line chart (I also used a second y-axis) and "bar" for the two bar charts.
You probably tried using a second dimension, I think this is problematic because you don't want it to apply to the line chart (and this results in a non-stacked bar chart).