Subreddits like r/RandomActsOfGaming or r/steamgiveaways are great resources. Users often post "random key drops" where they paste a code and the first person to see it gets the game.
These sites (like SteamGifts or Lootbar.gg giveaways) actually work. You enter, you might win a key. However, the "random" pool is filled by users dumping unwanted bundle leftovers. You’ll get 10 copies of The Howitzer Test Range before you get Elden Ring .
When obtaining free Steam keys, remember: