The "Republic of Gamers" (ROG) sub-brand of ASUS is targeted towards gaming enthusiasts, and the newly released ROG Phone 3 offers everything a mobile gamer can dream of. Besides featuring top-of-the-line specifications, such as Qualcomm’s flagship Snapdragon 865 Plus SoC, up to 16GB of LPDDR5 RAM, and 512GB of UFS 3.1 storage, the ASUS ROG Phone 3 also comes with three months of free Stadia Pro subscription. The Taiwanese OEM even allows tinkerers to fiddle with low-level kernel parameters using ROG UI's "X-Mode" in order to get the most out of the CPU and the GPU. In case you want some serious aftermarket developments like building TWRP or port an AOSP-based ROM, then you’ll be happy to know that ASUS has already released the kernel source code and the official bootloader unlock app for this device.
ASUS ROG Phone 3 XDA Review: The King of Gaming Smartphones is back
As a matter of interest, the unlocker app reveals the code-name of the third generation ROG Phone, which is "obiwan". Despite being "Force-sensitive" (pun intended), unlocking the bootloader on this phone voids the warranty, and also disables subsequent OTA updates. Moreover, the unlocking process automatically performs a factory reset, so it is highly recommended that you back up your data before proceeding.
Once you have an unlocked bootloader as well as have access to official kernel sources, you are free to get the ball rolling on building ROMs and kernels. ASUS has published the unified kernel source code for the Chinese and the global variants of this device in one archive, which is linked below. Unfortunately, you can't find a proper commit history in such a way of packaging.
ASUS has also released the official firmware packages for the ROG Phone 3, which will come in handy to restore the stock OS on your phone. Note that cross-flashing the global firmware on the Chinese unit (or vice-versa) may affect the ability to get OTA updates, so always grab the appropriate package for your model.