FP3 custom rom development based on released source code

It seems Verified Boot has been implemented by Fairphone
Can you please try to rebuild TWRP with these kernel defconfig flags disbaled

https://github.com/mstaz/android_kernel_fairphone_sdm632/blob/38de92e4740862caa6b79bc4816e6405a0c7b43f/arch/arm64/configs/fp3_stock_defconfig#L4888-#L4890

CONFIG_MODULE_SIG_KEY=“certs/signing_key.pem”
CONFIG_SYSTEM_TRUSTED_KEYRING=y
CONFIG_SYSTEM_TRUSTED_KEYS=""

You can follow this post here to build twrp yourself

For OS side you will have to unpack stock boot.img diff initscripts and fstab remove any verity checks here .

From your tree it seems to be okay https://github.com/mstaz/android_device_fairphone_fp3/blob/master/rootdir/etc/fstab.qcom#L36

I will my receive fairphone 3 in 1 week looking forward to join the development .