• Follow the instruction in this page

https://github.com/minimal-manifest-twrp/platform_manifest_twrp_omni

Remember to clone the correct version of TWRP based on what Android version your phone have! If your phone have Android 8.0, clone twrp-8.0 branch

• Copy working/(brand)/(device) folder to device/(brand)/(device) folder in TWRP sources

Example:

• brand name: xiaomi
• device codename: whyred

• Copy working/xiaomi/whyred to device/xiaomi/whyred in TWRP sources

• Open a terminal with the current dir pointing to TWRP sources root
• Then type

. build/envsetup.sh

to initialize the environment

• After that, type

lunch omni_codename-eng

where codename is the codename of your phone

• If that is successful, type

mka recoveryimage

to build the recovery.

If your device is A/B, use instead

mka bootimage

• If also that is successful, congratulation!
• Go to out/target/product/codename/ (codename is your device codename) and you will find your recovery.img

Go to 5. Boot the recovery image