Lightweight and good for gaming don't typically run in the same race, but it depends on what your definitions are. Honestly "lightweight" is not really an issue in this day and age, since the traditional heavy hitters (KDE/Gnome) are very similar to XFCE now. Ubuntu is essentially discouraged due to its reliance around the Snap architecture. Notoriously slow and unstable depending on the app, far from "lightweight". Ubuntu server is still great though.
Manjaro includes Steam and is pretty decent out of box, but Arch based and like most Arch distros, it can break if you're not careful. Arch distros are really fast, the AUR is incredible, and the wiki is the best online documentation out there. I use Endeavour myself.
PopOS! (despite its stupid name) is Ubuntu based, without snaps (last I checked), out of box setup for gaming, and supported by a larger hardware company that specializes in linux systems (System76).
Nobara is Fedora based, tuned specifically for gaming, rolling Fedora release, and built by one of the most influential developers of Linux gaming compatibility (GloriousEggroll).
Or as
@whm2074 states, why not Mint? It's very stable, well supported, easy to use, however, the Cinnamon desktop isn't nearly as lightweight as KDE, XFCE, or Gnome, and there's no Wayland support yet, if that matters to you.