The Closed Beta / Nightly update 21.6.16 has been officially released for Mi MIX Fold (codename is cetus). Before updating, please make sure you have downloaded the exact ROM matching your Xiaomi phone/tablet. In Fastboot mode, you can check model code by typing
fastboot getvar product in cmd/shell.
The firmware files posted here are all official Xiaomi ROM, xiaomiROM.com do not own and never modified those firmwares，you will always download the file from Xiaomi server.
You may interest in those contents: Mi MIX Fold ROM Topics Xiaomi Devices Index
Download Mi mix fold (cetus) China MIUI 12 21.6.16 Recovery ROM with Android 11.0. Firmware size is 4.0 GB.