How to find which platform a user is on (Mastodon, pleroma, etc)? Is there any way to find this?

Also, for some users the instance is not being displayed after their Mastodon handle. Initially i thought perhaps those users are in the same instance as me. But that doesn't seem to be the case. I don't have an example at the moment. Is it possible to find which instance a user is on, if the instance is not displayed on their handle?

@freemo tagging you as you might know this.