If you forget your wallet passphrase. However, it matters how the wallet is structured to access it using key:

1. Private Key: If you have the private key associated with the wallet, you can access the funds directly using the key, bypassing the need for the use of passphrase.

2. Seed Phrase: If the wallet was created with a seed phrase (mnemonic), the seed can sometimes also be used to recover the wallet. Depending on the application, the seed phrase may or may not be encrypted with the passphrase.

3. Encryption: If the wallet is encrypted with a passphrase, you would still need that passphrase to decrypt it, even if you have the wallet's private key.

If you only have the private key and the wallet is not encrypted, you should be able to access your Bitcoin. But if the  wallet is encrypted with a passphrase and you don't remember the passphrase, recovering the wallet becomes much more difficult without it, even if you remember the wallet key.