I haven't tried it but considering the weak CPU it might not be a pleasant experience.

But if you want to try it OBS is available in the software store and should at least work in desktop mode. Probably not in gaming mode.

Edit: Actually, I did something similar. I played Dungeons and Dragons in the browser and chatting through Discord with my friends. I recorded the sessions with OBS and at least that worked fine.

I haven't streamed using only the Steam Deck, but I've used it as a streaming computer running both OBS and my VTubing software, since my laptop is much too weak for it. I used OBS NDI (now DistroAV) to push the video to the Steam Deck. That experience was pretty fluid, though setting it up might've been a bit involved. (Flatpak for it exists now.)

OBS supposedly works fine, as long as the game isn't too demanding it should be solid enough.

i can't even get streaming from my steam deck to work over discord, much less twitch.

if anyone has successfully done it, I'd also love to hear it.