Steps for installation:

If you're already on OOS 11 then you can directly skip to Step 6. Backup your internal storage before proceeding.

1. Use MSM tool to flash stock OOS 10: https://onepluscommunityserver.com/

2. Then check for updates from Settings and update to the latest OOS 11.

3. If you don't see the OOS 11 update then you can find the zip on XDA.

4. Copy it over to your phone and go to Settings, Firmware, tap on the top right corner and select local upgrade.

5. After flashing it and booting into it, unlock the bootloader.

6. Download Havoc-OS v4.4 or newer and extract the payload.bin from the zip.

7. Use payload dumper to extract all the partitions from the payload.bin file. Download from https://github.com/ssut/payload-dumper-go/releases.

8. Copy the extracted images to the folder containing adb and fastboot tools.

9. Create a flash.bat file with the following content:

@echo off
title Fastboot Rom Flasher
:choice
set /P c=Do you want to wipe all the data (Recommended) [y/n]?
if /I "%c%" EQU "y" goto :wipe
if /I "%c%" EQU "n" goto :continue
goto :choice
:wipe
fastboot -w
goto :continue
:continue
fastboot --set-active=a
fastboot flash boot boot.img
fastboot flash dtbo dtbo.img
fastboot --disable-verity flash vbmeta vbmeta.img
fastboot --disable-verity flash vbmeta_system vbmeta_system.img
fastboot reboot fastboot
fastboot flash odm odm.img
fastboot flash system system.img
fastboot flash vendor vendor.img
fastboot flash product product.img
fastboot --set-active=b
fastboot flash boot boot.img
fastboot flash dtbo dtbo.img
fastboot --disable-verity flash vbmeta vbmeta.img
fastboot --disable-verity flash vbmeta_system vbmeta_system.img
fastboot reboot fastboot
fastboot flash odm odm.img
fastboot flash system system.img
fastboot flash vendor vendor.img
fastboot flash product product.img
fastboot reboot
pause

10. Boot your device to fastboot mode and execute the script.

11. If your device is stuck in a bootloop then go to recovery and format data.

Note: If at any point your device tries to boot into system while the script's running and hasn't been fully executed then hold Power + Vol Up + Vol Down until the device is babck in fastboot. TWRP will no longer work on Havoc-OS v4.4 builds and newer due to OOS 11 blobs. Please do not flash TWRP if encrypted.