In a medium-size bowl, combine the flour with the baking powder and salt.
Add the yogurt and mix the dough using a fork, hands, or spatula until slightly crumbly with doughy pieces.
Turn the dough onto a floured surface and knead into a smooth ball.
Divide the dough into 4 equal pieces.
Roll each piece into a 5-6 inch long, 3/4 inch wide log and form into a circle, pinching the ends together.
Mix the egg yolk with water and brush over each bagel.
Add toppings if desired.
Preheat the air fryer to 350°F and spray the basket with olive oil.
Place bagels in the basket about 2 inches apart.
Cook for about 10 minutes, checking at 8-9 minutes to prevent over-browning.
Remove and let cool 5-10 minutes before slicing and topping.
For gluten-free bagels, combine gluten-free flour, gluten-free baking powder, salt, yogurt, and egg white; mix and follow the same steps.