I have a simple bookmarklet that takes pocket highlights in current page and list them in your devTools console. No API keys required as everything is just DOM traversal.

I was also frustrated by their API not supporting highlights, I emailed their support and they replied exporting highlights is a good idea (Yes, Einstein) and they'll consider it. I love pocket TBH but this is really a PITA. So I spent sometime dabbling to create browser extension that let me copy highlights to clipboard, and ended up tuning down to a bookmarklet. Let me know if you want to try it, I can put it somewhere and will share the link.