That page also says “On Mac computers with Apple silicon or the T2 security chip, Optimized Battery Charging is on by default when you set up your Mac or after updating to macOS Big Sur or later.”
Maybe, you or a system update switched off that setting? Alternatively, the logic behind that setting may have ‘decided’ that you need 100% charge now (I think this setting isn’t just a “limit charging to 80%” flag, but tries to predict future power demands)
That page also says “On Mac computers with Apple silicon or the T2 security chip, Optimized Battery Charging is on by default when you set up your Mac or after updating to macOS Big Sur or later.”
Maybe, you or a system update switched off that setting? Alternatively, the logic behind that setting may have ‘decided’ that you need 100% charge now (I think this setting isn’t just a “limit charging to 80%” flag, but tries to predict future power demands)