I wrote a blog post about frost https://www.iroh.computer/blog/frost-threshold-signatures

For iroh, we use curve ed25519, while nostr is using secp265k1. So the linked code only works with ed25519 keys.

But other than that this transfers 1:1. You can take an existing key and split it into as many key shares as you want. So you can move to a multisig style approach while preserving your nostr identity.

You could take the existing code, replace https://crates.io/crates/frost-ed25519 with https://crates.io/crates/frost-secp256k1, and you would have a working co-signing setup for nostr keys.