If you type it like this you’ll get an instance agnostic link (at least on instances v0.18 and above, not necessarily in apps): /u/[email protected].
You can also select from a dropdown box on the website to send a mention, however this link goes to their instance rather than your own: @ChamrsDeluxe. The code for this is @[email protected], you can type this manually and replace any link text in between the square brackets, so generally [link text](https://userinstance/u/user).
The old pre-0.17 instance agnostic links were [link text](/c/community@instance) or [link text](/u/user@instance), but the new versions will automatically generate without link code:
/c/community@instance
!community@instance
/u/user@instance (does not send a mention)
Also, kbin doesn’t federate properly. You might not even see this comment over there…