More to note:
Try to avoid restoring apps backup using Titanium Backup. It may break things up.
Don’t restore system data using Titanium Backup! It will definitely break the current installation.
It is also discouraged to Restoring Apps + Data using Titanium Backup
1. Download Lineage OS for OnePlus 3 Android 7.1.1 Nougat
Download Lineage OS ROM for OnePlus 3
2. Download Nougat Lineage OS Gapps
Download Nougat Lineage OSMoreps
3. Installing Nougat 7.1.1 Lineage OS on OnePlus 3
How to Install Nougat 7.1.1 Lineage OS on OnePlus 3 and Adding GApps into Lineage OS
Transfer both the Custom ROM and Nougat Lineage OS Gapps packages to the internal storage of your device.
Power off your device and boot into TWRP Recovery mode.
Once, you are into TWRP Recovery main menu, you need to make a hard reset. From the TWRP main menu tap on the wipe button and select Advanced Wipe. Then select all Dalvik cache, System, Data and Cache options.
Flash the custom ROM now. Choose the Install option from the recovery menu and choose the ROM zip from the file manager.
Now, flash the Nougat Lineage OS Gapps package that you’ve downloaded before in the same way as you did with the custom ROM.
Reboot the device and enjoy Nougat 7.1.1 Lineage OS on OnePlus 3.
Now you know where you can download Nougat 7.1.1 Lineage OS for OnePlus 3 and install it on your smartphone.