If I publish my contracts, are they visible for everyone to see?
Yes, once published anyone will be able to see the smart contract from that point.
Is there a way to search for contracts published by others?
Published contracts are discoverable by the sharable URL or if they’re on the Explore page. It is not yet possible to search all published contracts, however.
If I publish my contract on thirdweb, can it ever be unpublished?
Published contracts are stored on the Polygon blockchain, thus once published, it is not possible to unpublish the contract due to the immutable nature of blockchains.