Why Doesn't Biden Tell China That U.S. Bonds Are a Bad Investment?

It happens to be true, since the dollar will almost certainly fall if they ever choose to unload their bonds. However more importantly, buying up government bonds is the way that China props up the value of the dollar against the yuan. Ostensibly the Obama administration's policy is that it wants the dollar to fall against the yuan. So why isn't Biden encouraging China not to buy up so many government bonds, and why isn't the Post asking this question?