Cryptographically random v4 UUIDs generated locally with your browser's crypto API. Bulk up to 100 at a time.
Yes. They come from crypto.getRandomValues via crypto.randomUUID — the same CSPRNG your browser uses for TLS keys.
Practically no. A v4 UUID has 122 random bits — you would need to generate a billion UUIDs per second for ~85 years to have a 50% collision chance.