I do not think the toolbar (or anything else regarding your workflow) has changed. There always was (and still is) only the Close Tab command on the toolbar (called Close Session and Disconnect in older versions). The Disconnect Session command (which only disconnect, but does not close) is (and always was, since added in 5.16) only available in the main menu and in the tab context menu.

I make it a practices to disconnect from a session when finished with transferring files, etc. Older versions of WinSCP had the capability of placing the disconnect button on the toolbar.

What is your use case for a frequent use of the Disconnect command?

Currently using WinSCP v6.1.2. Is there a way to place the 'Disconnect Session' menu item as a button on toolbar?

Any assistance would be appreciated.