platform_manifest_twrp_omni/twrp-extras.xml

<?xml version="1.0" encoding="UTF-8"?>
<manifest>
    <remote name="TeamWin"
            fetch="https://github.com/TeamWin"
            review="https://gerrit.twrp.me" />

<!-- TWRP lives in omnirom android-9.0 (not AOSP!) -->
    <remove-project name="platform/bootable/recovery"/>
    <project path="bootable/recovery" name="android_bootable_recovery" remote="omnirom" revision="android-9.0"/>

<!-- Include external Magisk repo for repack binaries -->
    <project path="external/magisk-prebuilt" name="external_magisk-prebuilt" remote="TeamWin" revision="master" />
	
<!-- Include TeamWin android_system_update_engine to build a good update_engine_sideload -->
    <project path="system/update_engine" name="android_system_update_engine" remote="TeamWin" revision="android-9.0" />
</manifest>