I may have missed this in the rulebook but as the title says how do you determine the CR of Starship battles and encounters?
Starships have Tier instead of CR. You can learn about how to calculate the tier of a starship encounter at the Archives of Nethys section on Starship Encounter Building
And on that page is a brief explanation of how the enemy tier vs APL converts into an average, challenging, etc. encounter.
Thank you so much that really helps