Hello,
No you don't need to downgrade.
Steps:
1) Unlock the bootloader of your phone
2) Boot in Fastboot and flash TWRP for your phone (
download link)
3) Boot in TWRP and install latest Stable Xiaomi.eu ROM for your phone
4) In TWRP, go in "Wipe" menu and tap on "Format Data" button (then type "yes" to confirm)
5) Reboot your device and wait a few minutes (after a ROM installation, first boot takes some time)