Installing LineageOS 17 on OnePlus One is very easy. It is based on Android 10 and works very well. I did this from a computer running Ubuntu Linux. One of the prerequisite is to install adb and fastboot on the computer and any necessary USB drivers.
Disclaimer: Installing any custom image on phone comes without guarantee. No risks are covered or compensated. Any loss is to be born by the phone owner.
The general instructions to install LineageOS 17 is given in below link
The essential instructions can be summarized to
- Take complete backup of your phone before moving to next step
- Ensure phone is charged more than 60%
- Download LineageOS 17 ROM from https://www.los-legacy.de/bacon
- Download Gapps (Google Apps) for LineageOS 17 from https://www.getdroidtips.com/lineageos-17-gapps/ [I was not able to download apps]
- Download and install TWRP recovery image from https://www.getdroidtips.com/install-official-twrp-recovery-for-oneplus-one/
- Unlock the bootloader using the instructions at https://www.getdroidtips.com/unlock-bootloader-oneplus-one/
- Once the bootloader is unlocked, reboot the phone and copy the TWRP image file, GApps file, and ROM zip file to your phone’s internal storage.
- Now reboot the phone to TWRP recovery mode.
- In recovery menu, tap on Install button > Install Image > Select the TWRP Image file from the location where you have moved earlier. Install the image to recovery partition
- Swipe to flash the TWRP image
- Once the image is flashed, reboot the phone to recovery mode once more
- In TWRP menu, select Wipe option
- Select Advanced Wipe > Select the data, system, vendor, cache. Then swipe to wipe it.
- Flash the ROM zip file from the Install option.
- The system is still in mounted state. Uncheck it & Remount system and vendor manually. Then flash Gapps zip file as well. Note: I did not performed this step as I was not able to download Gapps
- Reboot the phone and configure it as new one.
Hope it helps.