Similar old questions:
SMC reset didn't work for me, and turning the option off and on again didn't help either.
I am using a 15" 2018 MacBook Pro.
The sensor doesn't seem to be damaged as suggested in one of the answers as I can see some difference in reading when disconnected and connected back to the charger -
How do I fix this issue?
Since the laptop is assuming that it's connected to a power source, I feel that the battery is depleting faster than expected.
Update: I have observed that when I remove the plug it shows me the "charging" status for some time (3-4 minutes) and then switches to "not charging but plugged in" status. Further, I don't get the sound which denotes the charger is plugged in when I plug it.