In other places it would be called a Colonels' coup
Nah. The military is not involved.
You use the words nobility and Palace Guard in your post, yet we don't have a nobility or a Palace Guard either. So metaphors are good for you but no one else? Colonels' coup more or less describes what you were describing: people with some power, but not
the power choosing to overthrow.
What it is is the American equivalent of a vote of no confidence in a parliamentary system. Although we don't have formal procedures for that in the US system, it is functionally the same thing.
There's something lost though with this explanation you forward. Right now, Joe Biden is formally in power. The only way to remove Mr. Biden from being formally in power against his will is either 1.) conviction of impeachment, 2.) the 25th Amendment is invoked by his Cabinet, or 3.) death.
The talk about what is going on now is not Joe Biden formally in power, it's the term of the President from January 2025 to January 2029 and who the Democratic nominee for the 2024 general election is. It is Joe Biden's place on a private political party function on whether they choose to nominate him for the next 4 years. By the rules, he's won everything that binds delegates (by default as no one significant chose to run against him), and if he chooses to not step aside, to remove him they have to choose to change the rules governing the National Convention. That's not a vote of no confidence in a parliamentary system. The parliamentary term to use would be one from Australia where they call it a leadership spill.