Personal anecdata:

- Work MPB which I got 2021-12, 99% of the time plugged in because I was WFH, last time I unplugged it to return it to my employer, the battery was at ~95% of max capacity (as reported by MacOS)

- Personal MBP bought 2021-12, only plugging in when battery was low, and 1.5y later the battery was at 80% of max capacity

It was then that I investigated a bit and learned the trick of charging only up to 80%, which is something that MacOS does automatically when it's constantly plugged in which preserves battery life.

Since then, my personal laptop also stays plugged in most of the time, its battery is almost always at 80% and the battery hasn't decayed further.