Hi,
MetaMask only supports EVM-compatible networks. From what I see their docs state that Alephium is EVM incompatible, so you won’t be able to add that network in MetaMask directly just like you can’t add for example Solana or Polkadot either.
If a token exists on a network that MetaMask does not support, but there is a wrapped version of that token as an ERC-20 token, you can hold that wrapped token in MetaMask. This is because the wrapped token operates on the Ethereum network (or another EVM-compatible network). Essentially, the original token is “wrapped” into a new form that works on Ethereum, allowing you to manage and use it with your MetaMask wallet.
Please make sure if the token has a wrapped version that you have the right token with the right contract address, always be careful who and what you interact with online and always do your own research before doing anything.