They are trying to navigate between inflation and deflation now to avoid a collapse to one of both extremes. Let's see what happens

TomK

So, the reason no one is freaking out is based on the assumption interest rates will be cut in 24 and head downwards again. Thus, as you say, inflating their bond assets bought via QE. And eradicating the losses.
But if inflation heads upwards again, cutting interest rates and more QE wont be an option... And the losses will materialise (already happening with the BOE which is selling bonds, at a loss, back into the Gilts market).
Hell of a dicey strategy.  Maybe our regulators could have a word about managing risks?!...😀

shado_op

Bank of Japan Grapples with Record Unrealized Losses 

It's the same with all the cb. At a point they need to grow their balance sheets by inflating their assets again (bonds or gold)