Irving Finkel of the British Museum posts on YouTube, mostly on cuneiform related topics. He posted one video about unwanted diaries . Due to his lobbying, the Bishopsgate Institute will accept donations of personal diaries, no matter who they're from. I'm re-listening to the video to be sure that they will take non-UK diaries.
Ah! He hasn't said so outright, but one of the diaries he presents as an example is from America. So I could, theoretically, send Grandma Lil's diaries to Bishopsgate. Reading them depresses me. I may mention why later.
The Great Diary Project has a website: https://www.thegreatdiaryproject.co.uk/. Their address is: 230 Bishopsgate, Spitalfields, London EC2M 4QH, United Kingdom.
He makes a point of stressing that none of the institute's diaries were written by politicians.