Use the .displayName extension

lib/pages/instance.dart

@@ -7,6 +7,7 @@ import 'package:lemmy_api_client/v2.dart';
 import 'package:url_launcher/url_launcher.dart' as ul;
 
 import '../hooks/stores.dart';
+import '../util/extensions/api.dart';
 import '../util/goto.dart';
 import '../util/more_icon.dart';
 import '../util/text_color.dart';
@@ -363,10 +364,7 @@ class _AboutTab extends HookWidget {
               ),
             ),
             ...site.admins.map((u) => ListTile(
-                  title: Text((u.user.preferredUsername == null ||
+                  title: Text(u.user.displayName),
-                          u.user.preferredUsername.isEmpty)
-                      ? '@${u.user.name}'
-                      : u.user.preferredUsername),
                   subtitle: u.user.bio != null
                       ? MarkdownText(u.user.bio, instanceHost: instanceHost)
                       : null,

lib/pages/users_list.dart

@@ -2,6 +2,7 @@ import 'package:cached_network_image/cached_network_image.dart';
 import 'package:flutter/material.dart';
 import 'package:lemmy_api_client/v2.dart';
 
+import '../util/extensions/api.dart';
 import '../util/goto.dart';
 import '../widgets/markdown_text.dart';
 
@@ -42,10 +43,7 @@ class UsersListItem extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) => ListTile(
-        title: Text((user.user.preferredUsername == null ||
+        title: Text(user.user.displayName),
-                user.user.preferredUsername.isEmpty)
-            ? '@${user.user.name}'
-            : user.user.preferredUsername),
         subtitle: user.user.bio != null
             ? Opacity(
                 opacity: 0.5,