Place chicken breasts in a multi-functional pressure cooker (such as Instant Pot®). Add onion, celery, garlic, coconut milk, mayonnaise, ranch dressing mix, hot sauce, butter, and apple cider vinegar. Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 20 minutes. Allow 10 to 15 minutes for pressure to build.

Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid. Shred chicken using 2 forks.

Select saute setting and stir in 1/4 cup nutritional yeast. Simmer for 5 minutes. Transfer to a serving dish and sprinkle with remaining 1 tablespoon nutritional yeast.

Serve with sliced celery, red and yellow bell peppers, and cucumbers for dipping.