These sites collect lots of entries into one convenient site. Some are for games on Steam, like SteamDB, Steambase or ProtonDB, others are for user customization options, like Steam Grid DB or Steam Deck Repo.
ProtonDB is a collection of over 100,000 gaming reports from other gamers as they test games with Proton on Linux and provide aggregate scores of how well games perform. A growing pool of suggestions provides tweaks that you can try to get games working while Proton continues development. In addition to this, you may explore the Steam game catalog on this site to browse and discover a wide range of titles that were previously unavailable for use on Linux.
SteamDB is a database of everything on Steam. Important note SteamDB is a hobby project and is not affiliated with Valve or Steam.