This is the death nail in the coffin of Twitter

[Old Crow]

37. This is a colossally stupid move on Musk's part.

Also, as a former copyeditor, I have to comment on the usage error in the post's title. I've never heard of a "death nail" -- seems to be a conflation of two separate expressions, namely "death knell" (the tolling of a bell to mark someone's death or, more loosely, an omen of imminent doom) and "nail in the coffin" (something that indicates that something will fail).

Suggested titles (if I were copyediting it): "End of block feature is one more nail in Twitter's coffin" or "Twitter's death knell: The end of the block feature."