What I did:
Attached a MindNode mind map file to an existing note.
What happened:
Neither clicking on attachment thumbnail nor selecting Open from context menu opens MindNode.
What I expected:
Opening attachments works with other applications (Project 365 [MS project clone], Excel, PDFs, Numbers). I expected the MindNode file to open.
Things that might be helpful to know (Agenda version, OS and model, etc):