The Internet Archive accepts donations (any size, variety of media, definitely including books), according to the information on this page:

https://help.archive.org/help/how-do-i-make-a-physical-donation-to-the-internet-archive/

However, while they intend to digitize what they receive (it is, after all, their whole purpose to digitize stuff and make it available), they do not promise to do so... whether, and when, depends on funding and, I assume, their decisions about priorities. They do promise to hold the original books.

Also, they want donations only of what is not already available, so there would be a need to check, book by book, whether it is already on-line (in their collection? on the Internet anywhere? not clear). Presumably this could be very time consuming.

The page linked to above includes a link to a donations form for further inquiries and a link to a webinar about the process.