Hi there! I understand you're having trouble loading the Allegiant app on your Mac running OS X 10.15.7. To help you better, could you tell me a bit more about what happens when you try to load the app? For example, does it freeze, show an error message, or just stay stuck on a loading screen?

In the meantime, here are some general steps we can try to get your Allegiant app loading properly:

1. Check Internet Connection: Make sure your Mac is connected to a stable internet connection. Sometimes slow or intermittent connectivity can cause loading issues.

2. Quit and Restart the App: If the app is open but stuck, try quitting it completely (using Command + Q) and then reopening it.

3. Restart Your Mac: A simple reboot can clear temporary glitches affecting app performance.

4. Update the App: If you have the Allegiant app installed via the Mac App Store, open the store, check for updates, and install them if available. Newer versions often fix bugs.

5. Clear Cache or Temporary Files: On macOS, you might not have a direct way to clear app cache for all apps; however, quitting and restarting usually helps. If the app saves its cache somewhere, you could try clearing it via the Library folder, but let's save that step for later if needed.

6. Reinstall the App: If issues persist, try deleting the app and reinstalling it from the Mac App Store. This often resolves corrupted app data problems.

If you let me know if you've tried some of these steps already or if the problem shows any specific error messages, I can guide you further. Also, if the app is a web-based app and you're accessing it via a browser, clearing your browser cache or trying another browser might help.

Are you using the Allegiant app downloaded on your Mac, or are you accessing Allegiant services through a browser? Let me know!