Behaviour properties bar is grayed out and I can't edit - any solutions?
Because there is no instance in your layout.
Open layout and add one instance to edit.
I'm really sorry but I'm quite new to construct 3 - how would you add an instance/what instance would you add?
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Find the instance on the properties panel and drag and drop it onto the frame to create a copy.
What you have on the right panel under "Object types" are objects. When you place objects on your layout, you get object instances.
When there are no instances, you can't change their values. Please read the documentation, this is a pretty important concept:
construct.net/en/make-games/manuals/construct-3/project-primitives/objects/instances