Setup takes about 30 seconds, one time only. After that, the app opens normally every time.
Double-click TheAccountant-3.0.0-universal.dmg. A window opens. Inside it, double-click Install TheAccountant.
A warning box appears saying Apple could not verify the app. Click Done (not "Move to Trash").
Open System Settings (gear icon), then click Privacy & Security in the left sidebar.
Scroll down to the Security section. You'll see a message that TheAccountant was blocked. Click the "Open Anyway" button, then enter your password or use Touch ID. If one more box appears, click Open Anyway again.
The app installs and opens. From now on, just open TheAccountant from your Applications folder or Launchpad — no more warnings.
Open the Terminal app (press Cmd+Space, type "Terminal", press Enter). Paste this line exactly and press Enter:
xattr -dr com.apple.quarantine /Applications/TheAccountant.appThen open TheAccountant normally from Applications.