I saw that people on the dark web would sign their posts with a PGP key to prove that their account has not been compromised. I think I understand the concept of how private and public keys work but I must be missing something because I don’t see how it proves anything.

I created a key and ran gpg --export --armor fizz@… and I ran that twice and both blocks were identical. If I posted my public key block couldn’t someone copy and paste that under their message and claim to be me?