If I remember right, it was written for 3.4 but works in 3.5 as well.
There are no plans for a 4.x release right now, as I've found that Godot Dialogue Manager and Beehave both cover the original use cases I made this plugin for, so I highly recommend one or both of those if you want something like this in 4.x. I've also discovered Cognite and Godot Orchestrator as more general purpose visual scripting tools like this is, but I can't vouch for them as I have not personally used them.