There should be a way to add or modify Behaviors on an Object by using the Properties window. Coming from Construct, I loved having the Behavior variables exposed that I could change in a single click. It helps to prototype stuff quickly and is a huge QOL. In GDevelop, the Behavior variables seem to be 3 clicks away and cannot be looked at quickly. The old versions of GDevelop seem to have supported this before the UI rework.
I suggest the content of the Behavior window should be duplicated in the Properties window. The Behavior window can be kept as is. Users can decide to work with the Properties window or the Behavior window.