Librem 5 won’t have a TPM. It will have an OpenPGP smart card which you can use to securely store GPG secrets and perform secure cryptographic operations on-chip, so in some ways it will offer TPM-like features.
We are also looking into using an external Librem Key along with PureBoot to offer tamper-evident boot protection much like we have with our older Librem laptops that don’t have a TPM but do have PureBoot firmware installed.