@fooflington I use Alexandria
https://github.com/mvz/alexandria-book-collection-manager/
for me, the ISBN import has good days and bad days, so YMMV.
Recommend to give it a testrun before investing time and money into a solution for barcode scanning in bulk and then feeding the ISBNs to Alexandria (that's how I entered my books initially)
Since I tend to add less than a dozen books a year, when the ISBN lookup is not working that day I tend to shrug and just fill the hand full of fields manually