Open Discover or the default software store, search for Steam, install.

sudo apt-get install steam also works.

You can also use the .deb from the Steam website or the Flatpak, but I don’t really recommend either of those options.

It might be a little on the small side for you, but Hogwarts Legacy is pretty fun. There’s a ton of neat little side missions and secrets to find, and the world is a lot of fun to explore. You don’t need to know anything about the “Harry Potter” universe to play it. If you do, you might catch references, but it won’t make the game worse without knowing anything in advance. Overall, it’s a well-made cozy action RPG, the magic combat is surprisingly good, the world is gorgeous, the sound track is excellent, and the climax of the game is an extremely well executed epic-scale battle. The story is fine, not amazing, but works for the purpose of giving you a reason to progress the game. The character quests are actually better from a story perspective, and work well to give you plenty of quality diversion.

KUbuntu (not LTS) is a pretty close match. With a 6-month release cycle, it’s pretty close to SteamOS in the stabilizing cycle, and if you add the official KUbuntu back ports PPA you get stable updates to the KDE frameworks (so things like Wayland HDR support). It’s been working great for me on multiple computers, extremely stable, good performance, and basically no weirdness with games either.

USB-C probably can’t provide the necessary wattage.

As for the battery life, I have no idea. I have a Lenovo Legion all-AMD and it’s been quite good. The successor to mine apparently can last up to 9 hours for non-gaming workloads. It sounds to me like Dell messed something up here in a big way.

Is there no in-game V-Sync option?

It’s not.

If you’re buying for yourself, get what you like. If you’re buying as a gift, get what you know works.