And finally, Microsoft seems to have paid attention to EarTrumpet - at least in the latest test image of Windows 11 Insider Build 25281, the volume mixer in the system tray has acquired functionality very similar to this utility. Now the Audio section in it includes volume control in individual programs, which was pointed out by one of the developers of EarTrumpet, Rafael Rivera.
Microsoft has not yet officially announced this functionality, and in the latest test image it is hidden as experimental.