> without initially seeking my consent

That's just how SSH works. If you want to be pseudonymous, you should also generate a new key pair.

> That's just how SSH works

I know that. Just because SSH automatically sends my local $USER doesn't mean they have to report the value received in the SSH username automatically on the game platform to other users, without first having prompted me "your username has been reported as <greengreengrass>. Is it okay to show this?".

A simple flag in my user profile in the platform to say whether I've said that's okay or not.

Or instructions to advise people to choose their username /before/ first connect. These are reasonable, privacy-preserving things to call out in a good and user-friendly design.