Running GTK applications in XFCE as if in MATE

When running, for example, thunar in XFCE 4.18 it seems to be using a different version of GTK than when run in MATE 1.26. A difference is that MATE displays the Alt-key mnemonics (menu accelerators/access keys, the underlined letters in the window menus), while in XFCE this feature is gone because it was deprecated in GTK3. Even non-XFCE applications, like gimp, have the mneomics in MATE but no longer in XFCE.

Is it possible to run applications in XFCE (e.g. maybe with some LD_PRELOAD or LD_LIBRARY_PATH) so that they run as if in MATE?

What accounts for this difference between XFCE and MATE?