How to make your twrp boot without any vbmeta

Getting avbtool.py

Get it from here: https://android.googlesource.com/platform/external/avb/+/refs/heads/master/avbtool.py

Getting info from stock recovery.img

python avbtool.py info_image --image recovery.img

Setting up BoardConfig.mk

# Be sure to have these flags as they are avb related
BOARD_AVB_ENABLE := true
BOARD_AVB_ROLLBACK_INDEX := $(PLATFORM_SECURITY_PATCH_TIMESTAMP)
BOARD_AVB_RECOVERY_KEY_PATH := external/avb/test/data/testkey_rsa4096.pem
BOARD_AVB_RECOVERY_ALGORITHM := SHA256_RSA4096

# Set this according to the info given by avbtool.py
BOARD_AVB_RECOVERY_ROLLBACK_INDEX := 0
BOARD_AVB_RECOVERY_ROLLBACK_INDEX_LOCATION := 0
BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flag 0

Setting up the device tree in general

Remove any mkbootimg file if it is present.

Add this bootimg.mk to your device tree.

Be sure to reference to it in the device tree like:

BOARD_CUSTOM_BOOTIMG_MK := $(DEVICE_PATH)/bootimg.mk

Also check that these flags are correct and corresponding to your device:

# Kernel
TARGET_PREBUILT_KERNEL := $(DEVICE_PATH)/prebuilt/
TARGET_PREBUILT_DTB := $(DEVICE_PATH)/prebuilt/
BOARD_PREBUILT_DTBOIMAGE := $(DEVICE_PATH)/prebuilt/
BOARD_INCLUDE_DTB_IN_BOOTIMG :=
BOARD_INCLUDE_RECOVERY_DTBO :=
TARGET_KERNEL_ARCH :=

# Boot
BOARD_BOOT_HEADER_VERSION :=
BOARD_BOOT_HEADER_SIZE :=
BOARD_KERNEL_BASE :=
BOARD_KERNEL_CMDLINE :=
BOARD_KERNEL_IMAGE_NAME :=
BOARD_KERNEL_PAGESIZE :=
BOARD_KERNEL_OFFSET :=
BOARD_RAMDISK_OFFSET :=
BOARD_KERNEL_SECOND_OFFSET :=
BOARD_KERNEL_TAGS_OFFSET :=
BOARD_DTB_OFFSET :=
BOARD_DTB_SIZE :=
BOARD_MKBOOTIMG_ARGS := \
	--kernel_offset $(BOARD_KERNEL_OFFSET) \
	--ramdisk_offset $(BOARD_RAMDISK_OFFSET) \
	--tags_offset $(BOARD_KERNEL_TAGS_OFFSET) \
	--second_offset $(BOARD_KERNEL_SECOND_OFFSET) \
	--header_version $(BOARD_BOOT_HEADER_VERSION) \
	--pagesize $(BOARD_KERNEL_PAGESIZE) \
	--board "DummyBoard" \
	--dtb $(TARGET_PREBUILT_DTB) \
	--dtb_offset $(BOARD_DTB_OFFSET) \
	--recovery_dtbo $(BOARD_PREBUILT_DTBOIMAGE)