While the titlebar of the main Krita window shows an asterisk if the current focused document has unsaved changes, when multiple documents are open, there is no way to know which of them have unsaved changes other than checking them one by one. I believe adding the asterisk to the tab/subwindow title bar of each unsaved document will allow for easier readability of the current program status.
Created attachment 108705 [details] tabs display in 4.0 I attached a screenshot with what we currently have in Krita 4.0. Instead of a *, other applications are being a little more descriptive by saying it is modified. In the screenshot, the modified document is the inactive tab...so that should give you the information you need