I don’t think it’s the fact that it’s plugged in so much. I used mine plugged in pretty much all the time. It only charges to 80% but every once in a while, I drain it down to zero. I do live in a cooler climate as well and I probably don’t use my computer as much as most people.
I've got 90% on a 2020 bought one. I only plug it to charge it, rarely use it plugged.
But I'd say that how much it's used is also an important factor.