If the microSD card is not recording videos or cannot automatically delete old videos on the Xiaomi Smart Camera C201, please refer to the following steps to troubleshoot:
Check whether the Xiaomi Smart Camera C201 firmware and the Xiaomi Home App need updates.
Check whether the storage switch is turned off or if the recording mode is set to record only moving images.
Format the microSD card within the Xiaomi Home App. Formatting the microSD card will clear the videos. You can back up the videos before formatting.
If the Xiaomi Home App cannot format the microSD card, use a card reader to format it on a computer. After formatting, power off the camera and reinsert the microSD card.
If the microSD card cannot record videos, the issue can be related to the card itself. Try replacing it to see if the problem persists.