Event like: "Field value has changed" to control state of other fields of the entity, while creating / editing entity

As ECA is a tool operating on the server as a backend processor, it never gets anywhere near the web browser of the users. That's why there are no events for what you're looking at.

Your requirement needs a solution that gets javascript in the browser to recognize such field value changes and then take some action. The mentioned module "conditional fields" does that, but you could define such stages with eca_form as well. See also the similar issue 💬 Conditional fields functionality Fixed

Thank you for your explanation. I'd use "Conditional fields" as recommended here. Thank you.

Automatically closed - issue fixed for 2 weeks with no activity.