Optimized battery charging in Big Sur
There seems to be a severe problem/issue in Big Sur with the System Preferences > Battery > Optimized battery charging. This week I had two times the same situation. My MacBook Pro (MacBookPro14,3) showed the remaining battery at 4% and kept falling. So I attached it to the Power Adapter. The battery symbol in the menu bar showed a plug symbol instead of the typical thunder charging symbol. The MacBook refused to charge the battery in this critical situation. The battery went down to 1%, and macOS shut the system down and turned the machine off. At the first moment, I thought that the Power Adapter or the cable is broken. But this wasn't the case because, after the shutdown, the battery started to charge. After charging, I performed an SMC reset just in case. Today it happened again. It was the same situation. But this time, I opened the preferences and turned off the "optimized battery charging". The MacBook started immediately to charge the battery.
MacBook Pro 15″, macOS 11.2