Add the nutmeg, allspice, cloves, star anise and cinnamon to the bottom of a pot (or to a skillet for Slow Cooker instructions). Toast over medium heat for 2 to 3 minutes, stirring occasionally, until fragrant.
Turn the heat to low. Pour in the apple cider and bring to below a simmer, just barely bubbling. Warm for 1 hour on low heat (don’t let it simmer). Skim off any particulate if desired, or stir to re-incorporate it.
Place the apple cider in the slow cooker or Instant Pot (pressure cooker) with the spices. Cook on low for 3 hours OR Normal using the Instant Pot “Slow Cooker” setting.
If using, stir in the rum. Garnish with orange slices and cranberries, then serve.