In France it really depends where you are. IME Access to “alternative” foods - whether vegetarian, vegan, dairy free or gluten free - can even differ from village to village in the same area.
we visit france a lot and have at various times required vegetarian, DF and / or GF food.
i cannot imagine being vegan here. And as for vegetarian - you really need to find some recommended cafes / restaurants and then book accommodation nearby!
or self cater
currently we are in southern france about an hour east of where we usually go. Finding both GF and DF food in the supermarket has been a problem. Some supermarkets have nothing
my DD has been a little upset by it as on previous trips we have found plenty of DF desserts without soya. This time - we eventually found 1 supermarket with only a couple of suitable items - she enjoyed them (thankfully!).
we have a friend who ordered cheese on toast without bacon - and was clear with the waiter that they were vegetarian and so didn’t eat meat so could not eat bacon - their food arrived with bacon on it!!! When challenged the waiter said it was “wafer thin” and part of the dish so they should eat it!!!!!
The French are very proud of their cuisine and generally eat very high quality and unprocessed food. Therefore vegetarianism has not been a huge thing here because there are not the worries about the conditions animals live in.
I understand access is getting better but seems very omelette and cheese based when out n about!
hope you found some suitable places to eat.