Goodreads has been in the process of deprecating their API for years now. As of December 2020 they stopped issuing new API keys, but let existing ones keep working.
It’s not documented, but even with an existing API key, somewhere around mid-2022 they crippled the API so that it no longer returns many properties about books being returned – e.g. publication year or number of pages. It’s still possible to extract reviews, but that’s about it.
I recently restyled this site’s /reading section which had still been syncing from Goodreads (although I’m about a year behind on reviews). The API still technically works, but given the certainty of deprecation and truncated functionality, it seems about as good of a time as any to move back to a flat file.