Overlays should be possible to add when using RetroArch cores. Setting them up is currently out of scope for our wiki (as not many of our maintainers use overlays) so if you are interested in displaying them you'll need to research the steps to do so directly.
A good place to start is here: https://docs.libretro.com/guides/libretro-overlays/.
Overlays are not supported for standalone emulators. That said, if you are interested in developing the support to add them please check out how to start contributing here.