All my HEIC images are marked as invalid?

I'm trying to declutter my photograph collection, following this tutorial (https://dicksonneoh.com/blog/clean_up_your_digital_life/) but I'm already failing in the first step.

I've installed fastdup on a Raspberry Pi, and it tags all my HEIC files as invalid images (ERROR_LOADING_HEIC_IMAGE). I can't find any reference to that error, but the fact that it can't read any of them seems to point to an issue reading HEIC images, I would say. The images are, of course, valid (I can open them) and were taken with either an iPhone 8 or an iPhone 13.

How can I make fastdup read HEIC files? Nothing in the documentation seems to indicate that something needs to be done to do it.