I still hate the dedicated button replacing select, but I actually use the share button with the last 30 seconds a decent bit on the PS5. It's a cool feature to show a friend something without planning it in advance or actively recording and needing to delete old clips for space reasons, so I'd definitely support something comparable via Steam if it's done in a similarly convenient way.
Amd/Nvidia both have these features, and steam is unlikely to be able to beat the performance of those first party solutions but they might beat it on usability or some other set of features.