Juli Clover, MacRumors:

Macs running macOS 10.15.5 or later have a Battery Health Management feature to preserve the life of the battery, and occasionally, the Battery Health Management option will cause the Mac to pause its charging for calibration purposes.

And:

Battery Health Management features are available on Mac notebooks that have Thunderbolt 3 ports and that run macOS Catalina 10.15.5 or later. The option improves the lifespan of a Mac’s battery by reducing the amount of time that the battery spends at a maximum charge, which can cut down on chemical aging.

This Apple support document walks through the details.