How do I make my own behavior bundle? Mainly add contents.

I’m having a lot of trouble.

Go to the behaviors of an object.
Click behavior bundles on the left side of your screen.
Click new bundle (or add bundle, not really sure)
Click the new bundle to show its properties.
You can give it a name so you know what it is.
Click Edit contents to edit its contents

Unfortunately, you can’t drag&drop behaviors in a bundle. It used to be like that. But now you have to click edit contents.