These 21 words from old blockchain.info wallets are an internal recovery mechanism only - they are not BIP39 seed phrases (or any other type of seed phrase) and were not used to derive wallets or private keys. They only provide a back up mechanism for accessing your log in details to the old blockchain.info site, which has obviously since been replaced by blockchain.com.
If OP used a temporary email address, then his only two options for recovery are either if he backed up the .json file as Potato Chips has explained above, or trying to get blockchain.com's support to provide him access to his account. But given how terrible a platform blockchain.com is, I wouldn't be holding my breath.