Without another name change, I don’t think that phrase will ever go away, for the simple fact that X as a name is too short and nondescript. In speech, X could refer to a someone you broke up with, or it could just be the beginning of another word, serving as a prefix. In text, it could refer to the actual letter itself, or the close button on a window, or a placeholder, or something NSFW.
There’s simply too many ways that X can be interpreted that even if people associate Twitter with X, people will still specify “formerly Twitter” just to avoid confusion
Yes, you can add the Mozilla ppa and they offer a non-snap version. I think the Deb that you download from their website also isn’t snap, but I haven’t tried it