Hi @Andreas_Hegenberg, Great work here.
However I’d like to mention:
Your mockup seems quite “spaced out” and groups aren’t clearly marked...
1: Reduce paddings here and there? Ultimatley try aim for finder’s column view as I’m very comfortable with that.
2: Note that in finder, Folders have a triangle-arrow on the left side of their cell to denote that it can be expanded. It’s hard to see Groups here! Also, can it handle groups within groups?
3: Maybe add a list view toggle or an advanced mode for us users as dragging and copying various toggles doesn’t seem efficient in this view as you can’t have two groups open at once.
4: In your right hand column, I suggest tabs that switch it between Action/Format, andd maybe both for advanced users, if putting Actions at the top and Format under (like a paragraph) will be too cramped. I suggest this to always show (not show only if a trigger is selected). It would also be great to have a list view with this side column too!
Take a look at Tumult Hype Pro’s sidebar layout, as it’s a great example of a “Pro” sidebar thing. They also have similar goals such as formatting and scripting of elements which this sidebar handles, so it’s worth to take a look.
5: (extra objective 
)
Allow handling, selection and editing of multiple items
Anyway, I like UI design and I’ve been doing it for a while now as a hobby, so this is just some feedback for you!
If you do include a list view toggle, I’d love it if you included that thing in my thread before: