A Better Route Planner. (Frequently abbreviated "ABRP" by EV enthusiasts.)
While it's now owned by Rivian, it is still a separate entity and its plans often are different from Rivian app/in-vehicle-nav. Good for double-checking.
Also I'd recommend looking up any suggested charge stops on PlugShare and/or Chargeway to see actual user reviews of them to make sure they're reliable. I had Rivian and ABRP both recommend one route that would have required a stop at one specific charging station - with no other DC stations within reach by the time I got there. PlugShare said that station was *VERY* unreliable, with about half of all reports having it out of commission. I chose a different route.