An investment firm bought shares of Reddit (and some other privately held tech companies) at a certain value. In this instance they thought Reddit was worth ~$10 billion. This was August 2021. They now think it's only worth about half that. So they're having to update their books to indicate that they don't actually think they're holding $X of Reddit, but actually only about $0.5X of Reddit.
Idk if we should attribute this to the blackout as the article says "Worth noting that the vast majority of markdown in the value of Reddit and Discord holdings by Fidelity predominantly occurred last year".
It is interesting to see what they believe the value truly is but I'd love to see how much it was devalued recently.