Source: https://www.ghacks.net/2021/12/21/75-of-steams-top-1000-games-work-on-linux-now/
75% of the top 1000 games run on Linux now, and the figure is even higher, at 80%, for the top 100 games. Only the top 10 games are not well represented, as only 40% of them run on Linux without major issues according to the database.
Users have submitted more than 150,000 reports for over 21,000 games to the site. Of these 21,000 games, more than 17,600 are working according to the site.
Games on the database are ranked using a medal system. Platinum and Gold rated games run perfectly, and silver games may have minor issues. Bronze games may crash or have serious issues.
Borked games won't work at all or are unplayable, and native Linux games are just the opposite of that.
Protondb has a search feature that Linux gamers may use to find out if games that they are interested in work well on Linux. All games that match the search term are returned, which means that you can search for entire series of games, e.g. King's Bounty, Final Fantasy or Civilization, and get all reported games and their compatibility rating returned.