Cover the muffler, just let it cool first.

Cover the muffler opening for storage, but only after the engine has completely cooled down.

Blocking the exhaust does not trap moisture inside the cylinder. The moisture issue is real, but it comes from condensation forming when a hot engine cools. If you slap a cover on right after shutting off, you’re sealing that vapor in. Wait an hour, and it’s a non-issue.

The bigger reason to cover the muffler is keeping junk out. Sawdust, dirt, spiders, and even mice love an open exhaust port. A simple piece of tape or a rubber cap works fine.

For long-term storage, do the usual stuff too: empty the tank or add stabilizer, and pull the cord until the piston is at top dead center. But for the muffler question, yes, cover it — after it’s cool, not before.