esp32-c6 ADC value 4081 issue

[yeohwaisiang]

I have seen a few post regarding ADC reads keep returning 4081 instead of 4095, and in my test I realize that at about 3.3V/2=1.65V, the value I read is always 4081.
I tried ADC CH1,2,3,4 all returned the same result... 4081 from 1.6V onwards.
Why so weird?
Other opened thread that has nobody entertain to resolve are
1. viewtopic.php?f=13&t=33015&p=128745&hilit=4081#p128745
2. viewtopic.php?f=13&t=34668&p=116857&hilit=4081#p116857