My recipe calls for 4 eggs (Banana bread) but I only have 2. What can I substitute?

Don't know your timing or your pantry, but two more possibilities:
* soft tofu (2 oz/quarter cup for each egg) buzzed up with the liquids in blender, processor or mixer.
* aqua faba (liquid from canned chick peas). See link for more details
https://www.thekitchn.com/the-most-magical-egg-replacement-and-how-to-use-it-234588

Could you just halve the recipe?

What recipe are you using? most of my quick breads recipes use two eggs.

I always use the 2-1-2 substitute. 2T water, 1 t oil, and 2t baking powder. Otherwise, you could substitute 1 T ground flax with 3T water per egg.

Another 1/2 mashed banana. I have also used applesauce in baking to sub for eggs, about 1/4 cup for 1 egg. If the applesauce is sweet, you may want to reduce the sugar in the recipe.

Flax seed should work. Here's how to substitute: https://www.thekitchn.com/egg-substitutes-in-baking-try-95072