You will need a GPU to install the operating system. From that moment on you could remove the GPU from the system but for that the motherboard must allow startup without GPU, not all motherboards allow it.
Also keep in mind that if you ever need to log in locally you will have to reinstall the GPU at least temporarily.
i see, so at least i need some GPU to run it and boot for the first time.
and i guess my motherboard won't allow it without GPU.
is there any recommendation for lowest TDP GPU to install on my NAS? since the Ryzen 1600 already consume around 65W