Some of the most thought provoking reading I do lately is a couple of commentary emails:
"Money Stuff" by Adam Levine. Formerly just an email, now a column in Bloomberg Opinion, it's commentary on financial news by a former investment banker who likes noting how the day's trends relate to business fundamentals. Along the way, he explains the business of investment markets in more detail than I'm familiar with.
"Astral Codex Ten" by Scott Alexander. Formerly a blog and now published on Substack, focuses on whatever he wants but usually some aspect of the search for truth, usually by scientific means. Sometimes offers a passionately thoughtful critique of modern scientific method, using concrete examples (like the time where he showed science is often less proven than psionic powers, and argued this means science is doing a bad job) but ranges widely. Today's edition is one of a series of book reviews, some by readers rather than Alexander. Today's book is "The Wizard and the Prophet", which uses a comparative biography of two people as a way to examine the question of whether technology can solve our problems (the two people are Norman Borlaug, the Green Revolution wheat developer, and William Vogt, early US environmental advocate).
Both emails are lengthy, but entertaining / interesting.