MiFirm
Steps to install our ROM for first time from China ROM (All your data and files on internal storage will be deleted!)
- Unlock your bootloader by Mi Unlock tool https://en.miui.com/unlock/
- Download our ROM zip file
K30 4G:
V11.0.10.0.QGHCNXM https://mifirm.net/downloadeu/5927
20.1.21 https://mifirm.net/downloadeu/5886
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K30 5G:
20.1.16 https://mifirm.net/downloadeu/5928
- Unpack downloaded zip file in the PC
- Reboot your device to fastboot mode (press volume down + power)
- Connect to PC via USB cable
- Run fastboot installation script from unpacked zip according your PC operating system
For Windows OS windows_fastboot_first_install_with_data_format.bat
For Linux ./linux_fastboot_first_install_with_data_format.sh
For MacOS ./macos_fastboot_first_install_with_data_format.sh
- After reboot its done (first boot may take up to 10min)
Steps to install update of our ROM (All your data and files on internal storage will NOT be deleted!)
- Download our ROM zip file
K30 4G:
V11.0.10.0.QGHCNXM https://mifirm.net/downloadeu/5927
20.1.21 https://mifirm.net/downloadeu/5886
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K30 5G:
20.1.16 https://mifirm.net/downloadeu/5928
- Unpack downloaded zip file in the PC
- Reboot your device to fastboot mode (press volume down + power)
- Connect to PC via USB cable
- Run fastboot installation script from unpacked zip according your PC operating system
For Windows OS windows_fastboot_update_rom.bat
For Linux ./linux_fastboot_update_rom.sh
For MacOS ./macos_fastboot_update_rom.sh
- After reboot its done (first boot may take up to 5min)
Update via OTA:
Installation via OTA is currently not possible due to missing TWRP
Updater will notify you about new version and download it to your device for you
You have to copy it to your PC, unpack it and run fastboot_update_rom script
Enjoy.. 
Post source: https://xiaomi.eu/community/threads/guide-how-to-install-xiaomi-eu-rom-for-hmk30-hmk30-5g.54536/
Guide Redmi K30 4G Redmi K30 5G