Yeah, basically anytime a video or audio is being recorded, played, or streamed its from ffmpeg. It runs on a couple planets [0], and on most devices (maybe?)
[0] https://link.springer.com/article/10.1007/s11214-020-00765-9
[0] https://link.springer.com/article/10.1007/s11214-020-00765-9
That being said, if you put down a pie chart of media frameworks (especially for transcoding or muxing), ffmpeg would have a significant share of that pie.
Linux doesn't really have a system codec API though so any Linux video software you see (ex. VLC, Handbrake) is almost certainly using ffmpeg under the hood (or its foundation, libavcodec).