[IIsi50MHz]

Some occupied parts of the titlebar accept mouse-down-drag to move the window in MS Office apps, including:

document-name-dropdown, search-box, username, user-icon.

Elements that do not allow dragging the window, because they react to mouse-down, include:

application-icon, quick-access-toolbar, notifications-bell-icon, and the standard titlebar icons.

[pseudalopex]

This requires experimentation, memory, and conscious thought moving a window did not require previously.