When I click on an item ‘Send Message’ in the navigation menu, I want to create an object of entity ‘Message’ with attributes Email, Subject, Description. I want the Email attribute value to be auto filled from another entity ‘User’ which also has an attribute Email. How can I auto fill the Email attribute from another entity?
To do so, simply create a microflow behind the button that creates a Message object with the values you want to use from the user object. If it's the current user you want to use, you can use the default $currentUser. If not, you'll have to retrieve the user from the database first. The flow would end up looking something like this: