For a few versions now (maybe ever since 7.5.x, I don't remember, and rolling back too far is likely untenable due to complex dependencies), my scroll-wheel hasn't worked in libreoffice when USE="gtk" is set. I haven't noticed this in any other apps; for testing, I set USE="gtk" and installed x11-terms/mlterm and net-irc/hexchat and the mouse wheel worked fine in them. If I disable USE=-gtk and rebuild, scroll-wheel works fine again. I'm using fvwm-crystal with sloppy focus enabled. Can't try libreoffice-bin at the moment because it only supports python3_11 and I haven't finished moving some packages in my internal overlay up from 3_10 yet.
Additional data point: reproduced with both x11-libs/gtk+-3.24.35 and x11-libs/gtk+-3.24.38
Still having this issue with app-office/libreoffice-7.5.9.2