I downloaded the sketch below at the suggestion of the M5Stack AI chat assistant (https://chat.m5stack.com/) to test the beeps. They were very quiet. I changed the volume value from 8 to 255 and downloaded again. Still very quiet.

#include "M5StickCPlus2.h"
void setup() {
M5.begin();
M5.Speaker.setVolume(8); // Set volume to maximum (0-8)
(Second version: M5.Speaker.setVolume(255);)
}
void loop() {
M5.Speaker.tone(2000, 300); // Play a tone
delay(3000);
}

I then reinstalled the factory default demo sketch via https://docs.m5stack.com/en/uiflow/m5burner/intro. The button press beeps are quiet and can only be heard from about 5m away.

I also tried playing various wav files via the external speaker hat. They were almost inaudible from 1m away. Does anyone know what could be wrong please?