The system was released for smartphones in the Global and EEA regions with build numbers V184.108.40.206.RJCMIXM and V220.127.116.11.RJCEUXM, respectively. Unfortunately, the firmware still ships with MIUI 12. The update to MIUI 12.5 will come at a later date.
As for the list of changes, it is not long. The developers have worked on the security and autonomy of the device, as well as added some improvements to Android 11. For example, an updated section with privacy.
As usual, OTA is spreading in waves, so you have to wait for it to get to your device.