A layout_pageoffsets expression was added for print layouts which returns an array of Y coordinates for the top of each page in the layout. this allows users to dynamically position items on pages in a context where page sizes may change.
For example, to set an item at 2.5mm from the top of page 2 (for the data-defined position Y of a map item) :
@layout_pageoffsets[1] + 2.5
This constitutes a workaround for Issue 37567.