It's very hit and miss when trying to drag private variables from the Bolt Explorer window into the graph. Sometimes it works sometimes it doesn't. It's the same when using the alt key as the set modifier.

I've attached a video with some commentary showing the issue.

Steps to reproduce
* Create a new Bolt Class and Add a flow graph
* Create some private variables in your flow graph
* Open the graph and open Bolt Explorer (Window > Bolt Explorer)
* Try to drag your private variables into the graph.
Notice issue >> Sometimes this works some times it does not.

The workaround to this is to add them via the fuzzy finder but that is also painful at the moment as you need to wait for the units to reload.

Tested: Unity 2020.1.f1, Bolt 2.0.0a13, macOS