I’m very sorry to hear this too.
As Alex suggested, please make sure you are logged into iCloud with the same account. If there is data there, but not appearing, you could sign out of iCloud, and sign back in with the same account. Sometimes that helps.
Did you make a backup of your old computer? Eg. with time machine? Usually people have a copy of the data so they can transfer to a new computer. If you do have your old data, Agenda’s data should be in that too. We can help you find it.
Sync was designed for transferring data between two different computers. Although you can use it as a kind of backup, it wasn’t really built with that in mind.