I installed Funtoo last week from MATE installer, using mostly default/recommended things (except I added a separate partition for /home – I don't remember doing anything else unusual).

When I went to emerge i3 (my environment of choice generally), it required USE flag:

(i3-4.20.1)

>=x11-libs/cairo-1.16.0-r4 xcb

Adding to package.use worked fine, i3 emerged with no other issues.