The fact that the famous utilitarian became socialist-minded in his later years deserves to become better known.
It came to my attention several years ago, ironically as a result of a reading suggestion by a friend who describes himself as an ex-Marxist. He recommended a book by Ira Berliner featuring his concepts of "positive" vs. "negative" liberty. I wasn't impressed by Berliner as a thinker; for one thing, he never offered a sufficiently clear definition of "positive liberty" for me to be clear on what it was he was disagreeing with. For another, I think it's possible to make the case for Marxist politics purely in terms of "negative" liberty anyway.
But I'm still glad I read the book, because it also featured a talk given in commemoration of Mill, and it was from this that I learned of his latter support for the socialist idea and was led to read his book Principles of Political Economy and Chapters on Socialism.
Worth noting here is that, even before he started favoring socialism, Mill was expressing support for the idea of an inheritance tax on everything beyond a "fair start" for each heir, pointing to the British aristocracy as an example of the decadence that excessive hereditary wealth can foster.
Matt McManus's article in Areo, "John Stuart Mill, Socialist?": https://areomagazine.com/2021/05/12/john-stuart-mill-socialist/
His talk with Ben Burgis about the article: https://www.youtube.com/watch?v=G0por0j-FKU