I’ve never used multiple GPUs; I just use a single RTX 3090.
I think you may need to add -world_size 4 -gpu_ranks 0 1 2 3 like in this guide:
https://opennmt.net/OpenNMT-py/FAQ.html#do-you-support-multi-gpu
You would make the edit here. Argos Train is automation built on top of OpenNMT-py so you need to tell OpenNMT-py to use multiple GPUs.