The link does work, but it isn't the preferred way to link to communities in lemmy/piefed (and I think Mbin too).
Instance agnostic links look like this:
!<comm name>@<instance.tld>
For users:
@<user name>@<instance.tld>
The problem with linking to comms like the way you did is that it won't be opened in the user's instance (unless they use some client that does support resolving it).