Researchers have linked dietary data from over 55,000 individuals with data on the environmental impacts of the foods they eat. The team, from the Livestock, Environment and People (LEAP) project at the University of Oxford, found that the dietary impacts of vegans were around a third of those of high meat eaters. They also saw a 30% difference between high- and low-meat diets for most of the measures of environmental harm.
Plant-based diets are usually superior, health-wise, to meat-based diets.
There are a couple of nutrients that vegan diets at one point may have fell short in, like B12 and D being common examples, but at this point those are present in fortified vegan milks or breads.
The only other ones I can think of off the top of my head are a fatty acid present in fish, that is easily supplemented. Or less essential nutrients like taurine, which are also easily supplemented if one finds that they really need higher levels.
It can be difficult to get enough protein with vegan options for people who aren’t knowledgeable about the options.
There have been multiple scientific studies asking whether vegans get enough protein. The conclusion is always that they do. Here is one of them.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6893534/
I didn’t say they don’t, I said it’s difficult for people who don’t know how. You have to spend time on education when you go vegan.