As with when I tried it in BETA, 1.2 (now 1.2.6) the overlay doesn't work with my Witcher 3. I do have lots of mods but when going back the overlay works OK.

Looks like they're using an injector ala sweetfx, so using something such as reshade and having the overlay is most probably not possible.
Get rid of reshade, and you'll be able to use the overlay (tho it causes problems with the framerate so its best stick with your reshade preset instead.