@w depends what the video layer used is, the codec, etc
it's possible that many go the "easier" way and use a bad MJPEG or H263/lower codec, or maybe one of the xiph dot org libre video codecs

OBS can do it fine without GPU accel and it's FOSS too after all, I know there are people who use OBS to share their screen via RTMP over Telegram but that's a bit extreme