While there are vegan versions of lo mein that you can make, typical lo mein is not vegan.
The noodles in traditional lo mein are egg noodles, which of course have eggs in them.
So it’s already not vegan, before you consider any other ingredient.
Usually lo mein also contains vegetables and some sort of meat. Obviously the ones with meat are not vegan.
There’s plenty of Asian food that is vegan, so don’t be too discouraged that lo mein is off the menu for you at restaurants any more.