Some subreddits, like r/FreeGameFindings or r/RandomActsOfGaming, occasionally host legitimate key giveaways. These are posted by generous users who bought extra keys or received them from bundles.
While UL Solutions is unlikely to sue an individual for using a cracked key, you are still violating software copyright. The developers actively work on 3DMark. Paying supports continued development of new benchmarks. 3dmark License Key Reddit