There is basically no pre-modern society or culture that could pull off being vegan.

But there are plenty of vegetarian cultures that have lasted a while on eggs and dairy. Buddhism and Jainism have a history of vegetarianism tracing back literally millennia. Some European religions and groups refrained from eating meat from terrestrial animals, but many of these groups still ate fish.

Veganism in the pre-modern world wasn't feasible. It's feasible today mainly through our modern agricultural supply chains and modern understanding of nutrition: flaxseeds and chia seeds (or processed algae oil) for omega-3, cultivation of certain yeasts for B12, etc.