Combine chicken, beer, garlic powder, cayenne pepper, paprika, pepper, salt, and pumpkin spice in a slow cooker or in an Instant Pot.
For the slow cooker, cook on high for 4 to 6 hours, until the chicken is cooked through.
For the Instant Pot, cook on high pressure for 20 minutes and release naturally.
While the chicken cooks, add sour cream, chipotle, and adobo sauce to a blender. Blend until smooth. Set in the refrigerator until ready to serve.
Remove the chicken from the liquid to a large bowl. Shred the chicken using two forks.
Warm the tortillas in the microwave for about 15 to 20 seconds. To assemble the tacos, add pumpkin spice chicken to each tortilla. Top with avocado, black beans, chipotle crema, and pepitas. Serve immediately.