Right before left - the default rule
At any unmarked intersection - no signs, no traffic lights, no road markings - the default rule in the Netherlands is right before left. Traffic approaching from your right has priority over you. Traffic approaching from your left must yield to you.
This applies to every unmarked junction regardless of how the roads look. It doesn't matter if you're on a wider road, a busier road, or a road that looks like the 'main' road. Without explicit markings or signs, road appearance means nothing. Right-before-left is the universal fallback.
The rule applies per vehicle, not as a batch. If a car is coming from your right and another from your left, you yield to the car on your right and proceed before the car on your left. Each interaction is evaluated separately.