Microsoft is still working on making the new Skype app feature-equivalent to the older and now deprecated Skype 7 app, which means regularly adding back minor but much-loved features present in the old app.
The latest feature, which has just come to the Skype Insider Preview program on Windows 10 and MacOS, is a change to the UI that means that your list of conversations is always visible while in a Skype call. Previously while in a Skype call, the chat panel opened up on the left and prevented you from seeing your lists of conversations at the same time as the chat for the current call.
The chat panel is now also resizable.
The update takes the app to version 18.104.22.168 is available to Insiders, who can download the Skype desktop app here for either Windows or macOS, or the Windows 10 version from the Microsoft Store. The update should be coming to regular users in due order.