According to some data mining from the guy who runs SteamDB:
Steam is still working on clip recording. It supports background recording, includes timeline markers in supported games for various events.
Clips can be shared similar to screenshots, via the Steam community.
We don’t actually have any proof that this will be coming to Steam Deck yet, but I’m pretty optimistic that it would.
I recommend clicking through to the article, it has several screenshots showing how the feature will look.
On that note, that highlight feature that auto-captures kills and whatnot (on some games) is actually really awesome! Hopefully steam ends up having something similar