So you’re talking about forcing this Advanced mode to be open at all times when creating events?
And not allowing users to get out of it?
If so then in the PostEventBuilder component, I’d make a value transformer for initialScreen,a getter that reads this.args.model.initialScreen then is able to override it with the value transformer. So you’d always set initialScreen to advanced via the value transformer.
Happy to review a PR for core from you for the value transformer, I assume you have a custom theme you can hook this to already.