TLDR: You can sniff BitLocker keys in the default config, from either a TPM1.2 or TPM2.0 device, using a dirt cheap FPGA (~$40NZD) and now publicly available code, or with a sufficiently fancy logic analyzer. After sniffing, you can decrypt the drive. Don’t want to be vulnerable to this? Enable additional pre-boot authentication.
https://pulsesecurity.co.nz/articles/TPM-sniffing
https://github.com/denandz/lpc_sniffer_tpm