Hi there! I understand you're having trouble logging into Bridge Base Online on your Mac running OS X 10.15.7. Let's try to get this sorted out together.

First, can you tell me a bit more about what happens when you try to log in? For example:
- Do you see an error message? If so, what does it say?
- Are you using the BBO app or logging in through a web browser?
- Have you recently changed your password or account details?

Knowing this will help me give you the best guidance.

Meanwhile, here are some common steps that usually help resolve login issues on Mac:

1. Clear your browser cache and cookies if you're using a browser. This can remove old or corrupted data that might be interfering with login.
- For Safari: Click Safari > Preferences > Privacy > Manage Website Data > Remove All.

2. Try logging in through a different browser like Google Chrome or Firefox to check if it’s browser-specific.

3. Ensure your BBO app is up to date if you're using the app. Sometimes older versions have issues connecting.

4. Check your internet connection and try switching to another network if possible to rule out network problems.

5. Try accessing the new version of Bridge Base Online directly at www.bridgebase.com and click the “Play bridge now” yellow link, which sometimes resolves issues if the old app version doesn’t work properly1.

Could you please try these steps and let me know what happens? If you see any error messages or the problem persists, share those details and I’ll help you dive deeper.