Made changes based on the comments given by Joas

lib/Service/ParticipantService.php

@@ -1947,21 +1947,4 @@ public function getParticipantByActor(Room $room, string $actorType, string $act
 		$this->cacheParticipant($room, $participant);
 		return $participant;
 	}
-
-	/**
-	 * @param int $mentionId
-	 * @return string
-	 */
-	public function getLastUnreadMentionMessage(int $mentionId)
-	{
-		$query = $this->connection->getQueryBuilder();
-		$query->select('c.message')
-			->from('comments', 'c')
-			->where('c.id = :mentionId')
-			->setParameter('mentionId', $mentionId)
-			->setMaxResults(1);
-
-		$result = $query->executeQuery();
-		return $result->fetchOne();
-	}
 }

lib/Service/RoomFormatter.php

@@ -320,7 +320,7 @@ public function formatRoomV4(
 				$lastMentionDirect = $attendee->getLastMentionDirect();
 				$roomData['unreadMention'] = $lastMention !== 0 && $lastReadMessage < $lastMention;
 				$roomData['unreadMentionDirect'] = $lastMentionDirect !== 0 && $lastReadMessage < $lastMentionDirect;
-				$roomData['lastUnreadMentionMessage'] = ($lastMentionDirect !== 0 or $lastMentionDirect !== null) ? $this->participantService->getLastUnreadMentionMessage($lastMentionDirect) : '';
+				$roomData['lastUnreadMentionMessage'] = $lastMentionDirect ? $this->chatManager->getComment($room, (string)$lastMentionDirect)->getMessage() : '';
 				$roomData['lastReadMessage'] = $lastReadMessage;
 
 				$roomData['canDeleteConversation'] = $room->getType() !== Room::TYPE_ONE_TO_ONE
@@ -342,6 +342,7 @@ public function formatRoomV4(
 			$roomData['unreadMessages'] = $this->chatManager->getUnreadCount($room, $lastReadMessage);
 			$roomData['unreadMention'] = $lastMention !== 0 && $lastReadMessage < $lastMention;
 			$roomData['unreadMentionDirect'] = $lastMentionDirect !== 0 && $lastReadMessage < $lastMentionDirect;
+			$roomData['lastUnreadMentionMessage'] = $lastMentionDirect ? $this->chatManager->getComment($room, (string)$lastMentionDirect)->getMessage() : '';
 		} else {
 			$roomData['lastReadMessage'] = $attendee->getLastReadMessage();
 		}

src/views/Dashboard.vue

@@ -149,7 +149,7 @@ export default {
 				}
 
 				if (conversation.unreadMentionDirect) {
-					return t('spreed', conversation.lastUnreadMentionMessage)
+					return conversation.lastUnreadMentionMessage
 				}
 
 				return this.simpleLastChatMessage(conversation.lastMessage)