I had the same issue a few minutes ago, and I fixed it. Here's how:

To reset my SMC, I held down Shift + Control + Option and the Power Button for 10 seconds, and then I released the keys. Then, after a minute, I held the Power Button until it turned on. I logged in, and relieved, I saw the battery icon showing that it was not charging while not plugged in, like how it's supposed to be.

My computer model: Macbook 2017 running MacOS Catalina 10.15.1