In Museums or Archives dedicated to historical figures, their letters are often preserved and made public. In the 22nd century, perhaps you will be able to read the emails of today's celebrities.

And social media posts, recorded lectures etc.

And it will be a really complex process due to digital media not being created with long-term preservation in mind

At least one person is going to have their Reddit archives preserved.

emails

Please reassure me we will have remembered to spell mass nouns without the S by then. S.m.d.h