It’s true, just adding a prime tower won’t help if the printer doesn’t start printing on it first with a new filament.
In the case where the prime tower has already been printed for this layer, it is also ■■■■.
Is there any other solution that allows you to use leftover filament without losing print quality?
Some solution is certainly possible, after all, AMS detects when the end of the filament comes off the spool. If only the current layer was finished and the new one from the prime tower was started on a new filament, there would be little waste and there would be no loss in quality.