My Air 3 is still free from this issue after over 1.5 years. But I must admit I use it very rarely (it has only 35 charge cycles so that should give some impression how little it is used) and even then it is very light use so it does not get warm. What ever causes that reason, my wild guess - it is not time but maybe temperature combined with maybe battery shape changes...
My Air 3 recently developed a slight white spot after almost 3 years. I agree about temps likely being a problem.
I normally charge with an Anker 6- or 10-port 60W charger (max 12W per port). The white spot appears to coincide with when I started to fast charge my Air 3 more frequently with a 30W fast charger. Well, charger is 120W but the Air seems to be pulling a little over 30W max.