Same problem – and still miss the point. I have over two thousand records to create. I have the complete list of isbns, which I can parse to whatever format EndNote (or its competitors) will read. But I DO NOT want to search for each and every book, one at a time, on OCLC, LC, Google Books, or anywhere else.
ProCite used to do this. ProCite also read an existing bibliography and created a record for each entry. In 2013, in a backroom deal with Thompson-Reuters, EndNote bought (and discontinued) ProCite, so EndNote owns that code. Failure to implement that code, after many, mahy requests beginning that very year, , is simply yet another example of anti-competative practice.
If, by 2021, EndNote STILL has not updated/added this basic functionality – essential to every graduate student, faculty member, librarian, researcher, and used bookseller in the entire world – it is useless to me. I have bibliographies comprising HUNDREDS of entries. I have inventories comprising THOUSANDS of entries. If EndNote cannot do the obvious, it’s faster for me to write code that can. In which case, why subscribe to EndNote?