thanks for your inputs electrolux and carbonazza, actually the noise came from the nds crank arm, the 8 mm bolt was loosening itself during rides, especially when I was out of the saddle. I had to re-tighten it regularly on the fly during a bikepacking trip.
When tightened, the crankset did not spin freely but I do not know the source of the issue. I did not want to carefully investigated this, and replaced the ztto bb by a token ninja lite, and now I think this is working properly.