(photo: American Pie by Don McLean, sung above by three guys who are well behaved, model, middle-aged citizens… using an empty beer bottle as a microphone?)
Singing is neither cardio nor strength training. But when done by amateurs, it’s entertaining to the point of belly laughs, which is actually a mild form of core training.
Take what you can get.
Yet use this only as a short-term workout.
Get back to real cardio as soon as possible.