In Activity Monitor/Energy (Intel iMac, up to date) Usenapp is the only app listed (out of about 20 on my computer) with a ‘Yes’ in the Prevent Sleep column. All the others are ‘No’, with a couple no entry. This happens whether the app is an open window or not.
I’m not sure at all whether Usenapp does prevent sleep, but was just wondering why it might be.