Does it do this often? This is quite literally "printing money", right? Wasn't the Fed not supposed to be allowed to do that?

I'm guessing that if it doesn't do that, short term treasury yields will spike, and they don't want that to happen?

Doesn't this make treasury yields meaningless? If they're subsided by the Fed, then it means that nobody but them will buy them, since this subsidy means that short term treasuries are noncompetitive with other asset classes.

What am I missing?