It is not theoretical and there are companies doing the custom installation on demand.

There is quite a bit of public info on qwant and other search engines as well: https://www.sciencedirect.com/science/article/abs/pii/S0003682X20309762

Here is a device you can buy yourself, but this is on the lower end: https://creationnetworks.net/products/cambridge-sound-ds2530-70v-window-door-wall-masker-for-scif-secure-rooms-w-vol-control-retractable-cord-0815-900

Here is what one of the laser microphones look like, and you can actually even find and buy them (although not all countries permit it, but you can still buy them with a little bit of research :) https://pki-electronic.com/products/audio-surveillance-equipment/laser-microphone

Also an example of how its done to track your keystrokes (article paywall bypass included): https://archive.is/20251103180518/https://www.wired.com/story/infrared-laser-microphone-keystroke-surveillance/