Yes, you can use soap on cast iron.

Yes. Modern dish soap won’t damage a properly seasoned cast iron pan.

The “no soap” rule is a relic from when soaps were made with lye, which would strip seasoning. Today’s dish soaps (Dawn, etc.) are mild detergents. They’ll cut grease without touching the polymerized oil that is your seasoning.

That said, don’t go crazy. A quick scrub with soapy water and a sponge is fine. Don’t soak the pan for hours or run it through the dishwasher—that’s what actually ruins seasoning. Dry it immediately after washing, then rub a thin layer of oil on it while it’s still warm.

If your seasoning is flaking or patchy, that’s not from soap. That’s from thin seasoning, overheating, or metal scrubbing. Fix it by re-seasoning in the oven.

Soap away. Your pan won’t die.