The red rice phone keeps showing that the SD card is out of memory. What happened?

It's not that the SD memory card of your mobile phone is insufficient, but that the memory of your mobile phone itself is insufficient. After the software you installed is uninstalled, the residual files occupy the local memory of the mobile phone, so the SD memory will be insufficient when running. You can uninstall some software installed in the phone's memory, or the phone can be returned to the factory.