Hans van der Meer schrieb am 05.06.2021 um 17:59:
Why is there no effect of the yscale parameter in \externalfigure when the width-parameter is given? In the MWE it is the intention to stretch the height of the figure by a factor of two. But nothing happens. Leaving out the width does stretch the height, but then it becomes too wide.

Not all scaling and sizing combinations can be used at the same time.

To get both effects you can use \scale to stretch the figure to the desired height.