Bug introduced after 11.3, in or before 12.3, persisting through 13.0. Fixed in 13.2.0 or earlier.

Consider the following sample:

{Re, Im}[u'[t]] // Through // ComplexExpand

In v9.0.1 u'[t] is assumed as real:

But at least since v12.3.1 the behavior changes:

Is this a bug or incompatible change?

Is there a simple way to bring back the old behavior? (This answer of mine is broken at the moment due to the change. )