If your plan is emulation, Bazzite makes setting up either EmuDeck or RetroDeck very simple.

Just make sure to grab the Nvidia driver variant.

You can pick from KDE or Gnome, Bazzite does both.

A whole main, original thrust of Bazzite was to make it much more simple to set up emulation on a SteamDeck, uses a 'everything is flatpaks' approach by default, to keep things simple.

I run Bazzite on my Deck, works great for emulating older games, running modern games, I even set up a debian environment inside it via DistroShelf to do more complex dev type stuff.

With those specs, you should be able to run HL2 or a PS2 emulator just fine, I'd think, just keep the resolution at 1080p... maybe somethings you could take up to 2K, still be at or over 60fps, basically for games released prior to ~2006/7/8?