I sent my THETA/TFUEL tokens to Metamask and they are not displaying there.
THETA and TFUEL are not ERC20 tokens, they are native tokens on Theta blockchain. The tokens you sent actually went to the equivalent address on Theta blockchain. To access them, use the Metamask private key to open that address in the Theta web wallet. This can be exported from Metamask settings. It must be the Metamask private key, not the seed phrase.