undeveloped eastern seaboard in may

Ocracoke?

Maybe Tangier Island

A little farther south in Georgia is Jekyll Island. Most of this island is a state park with lovely beaches and bike paths. It also has the highly historic Jekyll Island Club Resort. By law 65% of the island is protected and much of it is wilderness. You can often see alligators and sea turtles and dolphins just off shore. There is a giant live oak which is 49 feet around. Spanish moss drips from the live oaks and there are palmetto trees.

Jekyll island my best idea too. It's nice if you can get a house rental, but don't stay on the busier side of the island in a hotel. Agree about the bike paths and the hiking paths on Jekyll island. Much of the island feels quite rural. And of course you have the historic area there too, where the gilded age millionaires hung out in the day.

Also, way further north, Chincoteague, Virginia could be nice. It's a small town on Virginia's eastern shore, located right next to the enormous Assateauge National Park. Which is the closest you can find to a wilderness beach on the east coast. The biting flies should not be bad in May.

i'm having an issue finding good rentals on airbnb - they all seem in a big community with a big collection of homes right next to each other. Any other sites you recommend at either jekyll or chincoteague - not looking to stay in a hotel or resort

If you want truly isolated and airbnb, good luck. The problem with the whole coast along the Carolinas and Georgia is that the protected areas usually are coastal swamps or parts of barrier islands (often quite small or narrow) that are popular destinations from Memorial Day onward. The entire East Coast lacks the history of public protected coastal lands that you find in the West or even in parts of the Great Lakes plus in the South, the Jim Crow history added another layer of keeping things in private hands. Many of these places have been weekend/summer destinations for decades---I had family who started going to the Outer Banks in the 40s and 50s. If you're doing early May esp. during the week, you'll have many fewer people than Memorial Day weekend onward and that would be your only plus.

"The entire East Coast lacks the history of public protected coastal lands" A very sizable portion of the coast between Assateague and Florida border, possibly even the majority of it if you were to count it all up, is undeveloped. Much of that is on barrier islands accessible only by boat, so people seem to ignore that it is there. In Georgia and SC for sure, the majority of the oceanfront is undeveloped. Almost all of the Virginia coast is entirely undeveloped. There is only about a 10 mile stretch of VA Beach/Sandridge that has any development. Everything south towards NC and north up the peninsula has nothing. A pretty good chunk of NC's as well.

I'm confused. You want "undeveloped" but you want to stay in an airbnb. Which is it? The Florida coast between Everglades City and Flamingo is as "undeveloped" as it was in Ponce de Leon's time. Maybe even more so since the Caloosa Indians are gone. Lotsaluck finding an airbnb there. Maybe OP should explain "undeveloped."
Jekyll Island is not "undeveloped."

It's tough to find accommodations on the Carolina coast without having a certain amount of development around you. It's basically a case of all or nothing.

That being said, you can look for places along the barrier islands (i.e., Kitty Hawk, Kill Devil Hills, Nags Head, Hatteras Island, Indian Beach, Emerald Isle, North Topsail Beach). Most of the ones I mentioned will not feel crowded. North Topsail Beach and neighboring Surf City are close enough to Wilmington to feel like entertainment, restaurants, etc are close by, but for me, it feels like being on Cape Cod back in the 1980s.

(Day beachtrippers from Raleigh, etc. tend to go to places like Wrightsville, Carolina, and Kure Beach -- easy access from I-40; more developed.)