Chess.com blocks many public proxy IPs. Even if you find a working proxy, it will likely:
If you are a tournament player trying to practice openings during a free period, a proxy will ruin your flow. The lag will cause you to lose games you should have won. chess.com proxy sites
Scammers know that "Chess.com proxy" is a trending search term. They create fake proxy sites to steal accounts. Here is how to spot a fake: The Core Issue & The Better Alternative Chess
For those preferring to use free proxy sites: chess.com proxy sites