To be clear, secp256k1 for public key name isn't precise

[ChristopherA]

You can call a method anything you want, but it seems you wanted to be explicit. There are multiple kinds of public keys possible with secp256k1, in particular there will be schnorr keys soon.

This is why we chose to call this public key "ecdsa-koblitz-pubkey" in the JSON-LD playground in the bitcoin signing section. Go to https://json-ld.org/playground/ and then pick person in the top tab row, then pick Bitcoin Signed in the bottom tab row to see a real Bitcoin (ECDSA Koblitz) Public Key.