Do the betta eggs breathe the oxygen from the bubblenest?
Betta eggs don’t need anything really. They’re equipped with everything the fry already need. I’ve seen eggs hatch without a single bubble present in the tank. Is your male betta fish still in the tank with the eggs? Generally, he would make repairs to the nest to keep the eggs from falling out, but if he’s not it’s still not 100% necessary. After the fry are born, they’ll get the oxygen they need from the water (because their labyrinth organ hasn’t developed yet). But I would suggest covering the tank with plastic wrap or a lid or something because once the fry start to breathe from the surface of the water, they could get sick and die if the air above the water is a different temperature from the water itself.