why are my airpods so quiet all of a sudden

Two places to look. Settings, Sounds and Haptics, Headphone Safety: if Reduce Loud Sounds is on with a lowish decibel number, that's your cap, and it has a habit of switching itself on after an update. Then Settings, Accessibility, Audio and Visual, and check the left right balance slider is dead centre. If both are fine it's almost always wax in the speaker mesh even when they look clean. A dry soft toothbrush over the mesh, then a tiny bit of blu tack pressed on and pulled off, lifts a surprising amount. Last resort: forget them in Bluetooth, hold the case button till it flashes amber then white, pair again.