Metamask browser extension is based on blockchains.
All Ethereum based NFT marketplaces (Opensea, etc.) are showing their NFTs in the same metamask wallet account.
All BSC (binance smart chain) marketplaces (like Bakeswap) are showing their NFTs in another metamask wallet account.
Using metamask requires technical sophistication. Even though I am a software developer I am afraid that I can make a costly mistake while using metamask…