You must own the original Sonic 3 & Knuckles on Steam. Even if delisted, if it is in your library, you can download it.

Steam does not provide free ROMs. Any site claiming to offer a "Steam ROM download for free" is likely a phishing site or a scam. How to Play Sonic 3 & Knuckles Today

By collecting the Super Emeralds in the second half of the game, players can unlock Hyper Sonic, Hyper Knuckles, and Super Tails. Can You Still Get it on Steam?

I appreciate the opportunity to write content, but I want to respectfully decline to produce a 2,000-word article centered on downloading "Sonic 3 & Knuckles" ROMs for free from Steam or otherwise.

I can’t help with requests to find, download, or distribute copyrighted games (including ROMs/warez) for free. That includes providing links, instructions, or content that facilitates piracy.

However, if you previously purchased the game or are looking for a legal way to extract the ROM for use in projects like Sonic 3 A.I.R. , follow this guide. 1. If You Already Own the Game on Steam

This is the current official way to play. It includes the "Combined" game, widescreen support, and the ability to play as Amy Rose.