Add the maxSegmentSizeBytes configuration when creating a stream.
It has to be in public record StreamSpec record.
See the java client as ref:
environment.streamCreator().stream("mystream-r").
maxSegmentSizeBytes(ByteCapacity.MB(500)).create();
except to have:
await system.CreateStream(new StreamSpec(stream)
{
MaxSegmentSizeBytes = xxxxxxxxx
});