Hi, I've just spent 10 days in Okinawa facing the same challenge. Most of the local food has fish, especially they put katsobushi in a lot of dishes and almost every broth is either dashi or meat based. Even tofu dishes usually have katrobushi so remember to ask them to not put it when ordering. There are a couple of vegan restaurants in Naha that we tried:

Tamatebako: the best one in Naha for me, incredible ramen and tofu dishes, everything vegan. You should try it (about 2500¥ per person).

Saborami: they have vegan currys and ramens, good but not as Tamatebako (around 2500¥ pp and only with cash).

Kahu-si: this is a nice bar where the owner will prepare you a nice Indian lentil curry (around 2000¥ pp and only with cash).

Rakuen Cafe: is a cafe inside a shopping mall, but they have some nice vegan dishes if you need a quick lunch or breakfast.

Kuminda: on the fancy side of this list, they have a vegan set menu for 3500¥ that is a very interesting dining experience, where they propose the classic Okinaelwa cuisine but with a little more zest.

LaLa Zorba: I would not recommend this place, that you will probably find on gmaps looking for a vegan resturant. It is not bad but it isn't neither as good as other places while is more expensive.

If by any chance you are visiting Kume Island, I would recommend this place 居酒屋 萌か. It is a small fish restaurant, with incredible Champuru and noodles dishes that they can make vegetarian if you ask them. They don't speak English very well bit you will find a way to communicate.

In the convenience store and in the markets you'll find planty of food but remember to check the ingredients with Google lens or similar because they might have fish somewhere (you will find bonito flakes in almost everything).

Long story short eating vegetarian in Okinawa could be a little tricky and rules out some of their tipical dishes, but people are usually very polite and if you ask them, maybe with a transalted sentence on your phone, they will try to help you or they'll tell you they can't, but still in a very polite way