The release of official LineageOs 15 nightly build is not yet announced, but unofficial build of LineageOS 15 (Android 8.0 Oreo) has already been available for many devices including the Redmi Note 4 (mido) Snapdragon variant. These builds are obviously based on the source code available on Github. Here is how to download and install LineageOS 15 (Android 8.0) on Redmi Note 4 (mido).
If you own a Redmi Note 4 (mido) Snapdragon variant and want to experience the latest Android 8.0 Oreo on it, then you can download and install the LineageOs 15 (unofficial) custom ROM on it. This build is almost fully functional, thanks to the XDA member thp@1997.
Currently, the ROM does not support VoLTE. Also, the Goodix and SELinux fingerprint reader is set to permissive. The rest of the system seems to be working properly, including Wi-Fi, Bluetooth, FM Radio, GPS, LED, Camera and of course, RIL (Calls, SMS, Data).
Disclaimer: Please follow this guide at your own risk. We can’t take responsibility for anything that goes wrong. This guide is intended for technically talented users only.
2. Boot Redmi Note 4 into TWRP (Hold Volume Up and Power buttons simultaneously. Continue to hold both buttons until the “MI” logo appears on the screen, then release).
3. In TWRP recovery, select Backup and create a Nandroid backup (recommended).
4. Now, select Wipe and then Advanced Wipe. Select Cache, System and Data partitions to be wiped and then Swipe to Wipe.
5. Go back to return to main menu, then select Install. Navigate to /sdcard, and select the LineageOS .zip package.
6. Follow the on-screen prompts to install the package. Once done, install Gapps zip file also.
7. Once installation has finished, return to the main menu, select Reboot, and then System.
Note: If you face any password related issue while booting, just format data via TWRP.
After booting, set up your new OS and enjoy LineageOS 15 (Android 8.0 Oreo) on Redmi Note 4. Any question? Leave it in the comment section below. (Source – XDA)