Sign arbitrary data with your SSH keys

I get that they're "public" keys, but I was surprised to learn (and from somebody other than github themselves) that ssh public keys are just available at that github.com/username.keys URL (without there being an option to disable it, it seems?). Did most people already know that? Probably fine but just surprised. Just tried searching their authentication docs [0] and I don't get any results for "public key url" either

https://docs.github.com/en/authentication?query=public+key+u...

Why would you want to disable it? They're not 'scare-quote' public, they're just public - analogous (kind of craply but workably) to 'distributing' your face, but not your passport/driving licence/etc.

The private key part is secret of course, never shared (that's where the analogy above breaks) but the public part is fine and desirable for everyone to have access to - that's how they verify that you signed something with your private key, how they encrypt a secret message to you.