TPM keys are protected by policies. A policy can be based on the system state (hashes), a password, or both. There are also complex policies using the Extended Authorization feature. If you don't care about platform state or configuration, then you can just set a key policy with just a password. The TPM will lock you out if you make too many incorrect guesses.

You can in fact put passwords on most TPM internal objects. See this example https://github.com/tpm2-software/tpm2-tools/blob/master/man/...