Currently you can only set a boolean to True or False via a dropdown list. We need the option to set it to another boolean via expression (such as setting an object's boolean to a function parameter.)
This is a pretty hard limitation and currently makes a simple 0 or 1 number variable the better option. I propose one of two solutions:
A) Add a "Set boolean by expression" action that has a text field instead of a dropdown list.
B) Add "expression" to the dropdown list which either creates or enables a text field underneath.
In the case of setting a boolean function param, I suppose it would have to be something like B..