At the moment when you open a second, or subsequent, database it uses the window used by the previously opened database. A workaround has been described elsewhere, but it would be good if that workaround wasn’t needed. Could we have menu items or a preference option to allow databases to be opened/created in a new window. This would preserve the workflow on the already open database, and allow an easy transition to the new one.
A new window is opened if the sidebar is hidden. But if the sidebar is visible and the database opened in the same window, then just use the contextual menu command “New Window”.