I would like to use the new MAME layout support for overlays, as described in https://github.com/libretro/RetroArch/issues/7419 and implemented in https://github.com/libretro/RetroArch/pull/8712 by @huwpascoe and @markwkidd
However, I don’t understand how to set it up. I am running lr-mame in RetroArch 1.7.6 on Linux, using the GL driver. I launch a MAME game and go into the RA menu, select Onscreen Overlay -> Overlay Preset and browse for a MAME artwork file. I have tried loading an artwork .zip file, and well and unzipping the artwork into a directory and selecting the .lay file directly. But the .lay file extension is not available for selection in the GUI.
I’m sure I’m doing something wrong, but cannot find any clear documentation on how to enable this. Can anyone point me in the right direction?