Hi there! I understand you're having trouble logging into the Global Blue app on your Mac with macOS 10.15.7. I'd like to help get this sorted out for you.

To start, could you tell me a bit more about what's happening when you try to log in? For example:
- Are you getting an error message? If yes, what does it say?
- Is the login button unresponsive or does the app crash?
- Have you been able to log in successfully in the past on this device?
- Is this issue happening only in the app or also when you try to log in on the Global Blue website through your browser?

Meanwhile, here are some initial steps to try that often resolve login problems:

1. Check Internet Connection
Make sure your Mac is connected to a stable internet connection. Sometimes login fails due to interrupted connectivity.

2. Update the Global Blue App
Since you’re on macOS, confirm that you have the latest version of the Global Blue app installed from the Apple App Store. Updates often fix bugs that affect login3.

3. Clear Browser Cookies if Using Website
If the login issue is on the website, your browser’s cookie settings may block the login. Ensure cookies are enabled for Global Blue sites. You can check Safari's preferences under Privacy to confirm5.

4. Restart Your Mac
A simple restart often clears temporary glitches affecting apps.

If you’ve already tried these, let me know what steps you took and any error messages you saw. That way, I can suggest more specific fixes or escalate it if necessary.

Looking forward to your reply!