Can you double check?
On my side, the generation is successful in NX.
$ ./tao-converter -k nvidia_tlt -d 3,544,960 -p Input,1x3x544x960,1x3x544x960,1x3x544x960 -o BatchedNMS -e /export/trt.fp16.engine -t fp16 -i nchw -m 8 yolov4_resnet18.etlt
Yesterday, another forum user also ran it successfully with this yolo_v4_resnet18.etlt.
See Error in Yolov4 engine conversion, - #41 by Morganh