Thank you for clarifying! I wrongly assumed that the new InDesign update would include the HEVC codec. I was also able to circumvent the $1 (just seems wrong for Microsoft to charge for a common codec, but I'll save that for MS forum). Per this article from HowToGeek, I was able to get a free version of the codec by pasting this url into my browser:
This free version can't be found using search feature in the Store, but it is still made by Microsoft. In addition, I installed this plugin. I'm now able to export PDFs from InDesign containing HEIC images.