XDA Thread

https://forum.xda-developers.com/xperia-xz2/development/recovery-twrp-3-2-2-0-touch-recovery-t3821597

Initialise the omnirom tree

• In a terminal window, enter the following commands:

mkdir omni_9.0
cd omni_9.0
repo init -u git://github.com/omnirom/android.git -b android-9.0

or for the minimal TWRP build environment

mkdir omni_9.0
cd omni_9.0
repo init -u git://github.com/minimal-manifest-twrp/platform_manifest_twrp_omni.git -b twrp-9.0

• Clone the local_manifests from GitHub using the following commands:

cd .repo
git clone https://github.com/MartinX3sAndroidDevelopment/omni_twrp_local_manifests.git local_manifests
cd ..

or for the minimal TWRP build environment

cd .repo
git clone https://github.com/MartinX3sAndroidDevelopment/omni_twrp_local_manifests.git local_manifests
rm local_manifests/twrp.xml
cd ..

• To download the code into the device repos created above, run the command:

repo sync

• To build the TWRP bootimage ("-eng" build)

. build/envsetup.sh;
export ALLOW_MISSING_DEPENDENCIES=true # Only if you use minimal omnirom twrp tree.
lunch;
make bootimage;