Listing using OpenSea usually removes your item from other Solana marketplaces while the listing is live. Two things cause this:
Your item moves into the marketplace escrow account, so your wallet no longer holds it onchain. Another marketplace may keep displaying an older listing for a while, but no one can complete a purchase there while your OpenSea listing is live.
Your listing is recorded by the Solana marketplace program OpenSea formats listings for, and other marketplaces do not read that program.
To list somewhere else, cancel your OpenSea listing first. Your item returns to your wallet right away, and you can list it wherever you like. Listings you created on another marketplace work the same way in reverse, so cancel those where you created them.