> FWIW you can have different handles in each Discord Server, it's under right click on the server icon > Change Nickname. Seems to affect mentions also (something that didn't until recently IIRC), so your original usertag should be completely invisible.

Nope. The different handle on a server is there for other people's benefit, not for yours. Anyone who sends you a direct message will see your actual Discord handle.

I can't fathom why it's implemented this way, but it is.