In April 2019 Panasonic unveiled a transparent OLED TV prototype housed in a wooden cabinet. Here's a nice video showing the display in action:
Panasonic has been showing transparent OLED display prototypes and concepts since 2016. This specific prototype was designed by Scandinavian based designer Daniel Rybakken in collaboration with Panasonic Design Kyoto.
We do not know who supplies Panasonic with its transparent OLED panels, but it is likely to be LG Display - which recently launched its commercial transparent OLED displays.