I'm thinking the OP has the laptop plugged in all the time - lead to overcharging in long term. Electronic battery doesn't like to be at 100% charged. You know why some new electronic comes at 50% charged from factory.
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You say that, but the battery life I've seen between two Macs I had plugged in for 99% of their life has been different:
2011 15" machine still had > 90 percent battery after 4 years and ~300 cycles
2020 intel air had 82 percent after 12 MONTHS and <100 cycles
Apple is either shipping way crappier batteries, or on the later intel machines with "optimised charging" it is limiting the charge by messing with the battery health reading which is perhaps used by the charging software on intel Macs to regulate when it stops charging the battery.
My bet is on the second one... because battery tech hasn't gone backwards to be degree that my two machines above would indicate (which, if anything had the 2020 air used on battery a little more frequently than the 2011 15").
Plus... the later model machines have improved battery management that the 2011 machine was not touted as having.
So again, my bet is that on the 2020
intel machines, apple is using the battery health reading to indirectly lie to the macOS charging software on those machines to get them to charge less when infrequently discharged, like al-dente, etc. do.
On the newer M1 based machines they perhaps have a different way or different hardware in the machine to regulate charge without needing to lie to macOS' charging driver via messing with the battery health reading.
Furthermore, on my M1-Pro, which I've had for around 6 months now, the battery health is 100%. It's used the same way I used the 2020 Air which was 82 percent after under 100 cycles in 12 months (M1-Pro has 30 cycles - 2/3 the discharge cycles over 1/2 the time - but that's because the battery life is so damn good).
edit:
how could I forget. I also have a 13" Pro 2015 machine with battery life just under 90 percent that has been used plugged in most of its life as per the 2011 and 2020 machines above.
Additionally - recently apple specifically mention on their site that battery management may show lower battery life than expected and that under 80% with the feature turned on is not necessarily a dead battery