At the moment you can see your NFTs only on Metamask Mobile. You can add NFTs as custom tokens in the web extension, but you will not be able to see them natively in the UI.
MetaMask Mobile displays NFTs under Collectibles. Please remember that some NFTs will not show up on the mobile app under Collectibles or may not show up correctly.
If your NFT doesn't show up automatically, try the following to make it appear:
Step 1 : Find the NFT's address. On most NFT interfaces you will find a blue hyperlinked value labeled "Contract Address". If you click on this, it will take you to the contract's address on Etherscan; at the top-left of that page, there should be an icon labeled "Contract", and to the right, a long string of letters and numbers. This is the address of the contract that created your NFT. Click on the "copy" icon to the right of the address, and you'll have it on your clipboard.
Step 2: In MetaMask Mobile, tap on the 'NFTs' tab, scroll down, and tap on the "+ ADD NFTs" link. Paste the NFT's address from your clipboard into the "Address" box.
Step 3: Find the NFT's ID. A collectible's ID is a unique identifier since no two NFTs are alike. You can find the NFT’s ID under "Details" on the NFT’s listing page on Swappable. Make a note of it or
Step 4: Copy it onto your clipboard.
Step 5: Paste the ID into the box marked "ID" in MetaMask Mobile, tap on the "ADD" button, and your NFTs should appear under the NFTs tab.