A battery optimization feature that allows users to set a battery charging limit is now available on the Steam Deck. While available only to those on the preview or beta channel, it is expected it will eventually be released to those on the stable channel.https://www.notebookcheck.net/Steam-Deck-gets-battery-charge-limit-feature-in-latest-beta-client-update.1013383.0.html
I doubt we'll see LFP batteries on mobile devices anytime soon, so all devices are NMC; and any device with an NMC battery should have had this feature for years now. My father's 2018 laptop has the charge limitor. I'm surprised that it has taken so long for it to arrive to the Steam Deck.