So my recommendation after reading tons of articles is to follow this video.
Essentially there are 2 ways how to move from a custom/vendor ROM to xiaomi.eu ROM. The method which is being used here in the video is to use the Chinese version of PC Suite and the recovery ROM.
- The video assumes the device is bricked but if it is not then it is enough just to turn the device into a recovery mode and use a (recovery) rom. To sum up, “flashing recovery ROM using Chinese version of Mi PC Suite in recovery mode.”
- Once done the second step is to unlock bootloader. Again the Chinese version helps. But this time I had to click twice, to unlock it.
- Download TWRP by cofface and follow its guidelines. End TWRP with “fastboot reboot” from command line.
- Lastly flash EU ROM using this.
Redmi 4/Prime/4A thread: http://en.miui.com/forum-119-1.html
[MIUI DEVICE TEAM] Flash / Unbrick Redmi 4/Prime/4A: http://en.miui.com/thread-408889-1-1.html
Bootloader Unlock – Solution for Redmi 4 Pro/Prime (unlocking stuck at 50%): http://en.miui.com/thread-429397-1-1.html
RedMi 4 Prime/Pro Twrp recovery: http://en.miui.com/thread-412204-1-1.html
Stable & Dev Rom: http://en.miui.com/download-320.html