Panasonic has been showing transparent OLED display prototypes and concepts since 2016, and in April 2019 the company unveiled its latest prototype - a wooden cabinet design:

At IFA 2019 Panasonic says that it aims to launch a transparent OLED display by next year as a commercial product. It is highly likely that this would be some kind of signage/commercial display.

Panasonic is using LG's 55" transparent OLED panels. LG started to produce commercial transparent OLED TV panels in early 2019. LG Display's transparent OLEDs feature a brightness of 150 cd/m2 (peak white brightness of 400 cd/m2) and a transparency of 38% and a color gamut of 120% NTSC. The display can optionally include touch functionality.

Panasonic - Rybakken transparent OLED concept photo

Merck - Advancing Display, Advancing LifeMerck - Advancing Display, Advancing Life