If you have a Linux PC with a TPM, you can use https://github.com/psanford/tpm-fido to create and "plug in" a virtual USB WebAuthn key whose secret is irretrievably stored in the machine's TPM. This effectively asserts that your specific machine is being used to enter a given site. However, it's important to remember it doesn't necessarily verify that *you're* present, or even if *anyone* is present at all, since the presence check is done via a software dialog and can be pwned along with the rest of the system.