The TPM itself does very little. It is simply used by the UEFI to verify that the digital signature of the OS image is valid, similarly to how a browser validates a server certificate using its own truststore.
A possible attack vector to compromise that functionality would be to tamper with UEFI. Since it is firmware, the operating system simply doesn't have the capability to so. Even when doing firmware updates, the OS must ask the UEFI nicely to apply a new firmware image, which is similarly verified using a digital signature.
All the above assume that there are no backdoors that allow an upper layer to compromise a lower layer.
Private key material is required for remote attestation, which makes it possible to prove certain things to an external party, for example the exact identity of the TPM. This feature is much more questionable.
That's a useful property, but you have to weigh it against a kernel that can be audited and patched.
The utility of patching your own kernel has to be carefully weighted against the security impact of doing so. If an attacker can take over the user account that compiles the kernel, they can make you install a compromised kernel. For example, by running a file system monitor that exchanges the kernel image with a compromised one as soon as it has been built.
The crucial problem is that the IT industry is more concerned about using it to enforce DRM instead of educating users so they can use it to retain ownership of their services.