This has long been considered one of Goodreads' big advantages: its massive publication database, ISBN and all. But recently Anna's Archive has been making quite a bit of noise about their considerable ISBN database:

https://annas-archive.org/blog/

This may well be a great opportunity to seed a Goodreads alternative.

I’ve always hoped that once we reach Goodreads scale, we’d be able to release database dumps like VNDB (https://vndb.org/d14) and Lichess (https://database.lichess.org/)

Since the metadata is contributed by volunteers in the first place, it only seems fair for it to be freely available rather than locked down.

My personal project, https://rate.house, is kinda like goodreads but for all types of media.

In case you don't know, there is also BookBrainz: https://bookbrainz.org/