The best way would be to arguably keep the key completely off the TPM and use remote attestation. There's some preboot products out there like WinMagic SecureDoc* that use a little Linux partition, spin up just enough to get a network connection up to a remote server, provide authentication services, and then send the Bitlocker key down, unlock the partition, and chainload onwards to Windows.
* I acquired an enterprise device on eBay and was VERY surprised to find this product on it as the preboot protector. Zero way to crack in from my end, so I applaud it. There's even some MFA solutions they offer around this! https://winmagic.com/en/solutions/mfa-windows-login/
https://pulsesecurity.co.nz/articles/TPM-sniffing
The best way would be to arguably keep the key completely off the TPM and use remote attestation. There's some preboot products out there like WinMagic SecureDoc* that use a little Linux partition, spin up just enough to get a network connection up to a remote server, provide authentication services, and then send the Bitlocker key down, unlock the partition, and chainload onwards to Windows.
* I acquired an enterprise device on eBay and was VERY surprised to find this product on it as the preboot protector. Zero way to crack in from my end, so I applaud it. There's even some MFA solutions they offer around this! https://winmagic.com/en/solutions/mfa-windows-login/