The server can't see what you copy

Only your devices can decrypt what you copy. The server can’t.

No accounts, no stored content. A device's identity is a key, so the server needs no user table.
Check fingerprints when pairing. Both screens show the same fingerprint; if anyone swaps a key, they won't match.
Every message is signed, so the server can't pose as your device.
The relay only forwards ciphertext. Relay credentials expire after 12 hours.
Private on the local network too. A device broadcasts an anonymous token that changes daily, so nobody can tell whose computer it is.