As per bug report #1867 on https://github.com/brndnmtthws/conky/issues/1867, ebuild requires new flag for BUILD_LUA_CAIRO_XLIB
This will be dealt with in the upstream issue tracker. https://github.com/brndnmtthws/conky/issues/1867
Splitting the xlib parts from the cairo library requires an update to the used lua scripts. So this is just a configuration issue. See https://github.com/brndnmtthws/conky/issues/1867#issuecomment-2088429729