Might be another smart woke guy who ended up badly. I don't, but below is from a quick search. Could be stories put out to discredit someone who knew too much, or just an old eccentric man being weird. Or is it much darker - wan't it also rumored that Twain a member of a satanic group called Hell Fire Club?
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In his 70s Mark Twain began to "collect" a group of adolescent girls, whom he called his “angel-fish”. Twain wrote at the age of seventy-three, “I collect pets: young girls—girls from ten to sixteen years old." One of them he called his “little witch”. The girls were the daughters of couples who ran in his same social circle He often met them on boats back and forth from England to Bermuda.
Twain put his own daughter in medical institutions. When she returned to Twain's home she was found drowned in the bathtub. His other daughter came to live there and banned the young girls, and Twains health seemed to decline rapidly. Weeks before Twain's death, his letters show he was obsessed with a young girl and jealous of her boyfriend.
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https://www.theparisreview.org/blog/2017/11/28/mark-twains-disturbing-passion-for-collecting-young-girls/
http://www.todayifoundout.com/index.php/2013/07/mark-twain-and-his-hobby-of-collecting-girls-from-10-16-years-old/