Hi there! I understand that you're having trouble with trailers not showing up on the Tubi app on your Mac running OS X 10.15.7. Let me help you get that resolved.

First, can I ask:
- Are you using the Tubi app downloaded on your Mac, or are you accessing Tubi through a web browser?
- Are trailers missing for all titles, or just specific ones?
- Have you noticed any error messages when trying to play trailers?

Once I have a bit more detail, I can tailor the steps for you better. Meanwhile, here are some general steps you can try that often resolve trailer playback issues on Tubi:

1. Restart the App or Browser
- If using the app, completely close it then reopen. If using a browser, close the browser window and reopen Tubi in a fresh tab.

2. Clear Browser Cache (if using browser)
- Sometimes cached data causes issues with loading trailers. In Safari on macOS 10.15, you can clear cache by going to Safari menu > Preferences > Privacy > Manage Website Data > Remove All.

3. Update the App or Browser
- Ensure your Tubi app is up to date if using the app. For browser access, check that your browser is the latest version.

4. Check Network Connection
- Make sure your internet is stable and reasonably fast. Trailers are short videos but still require good connectivity.

5. Try a Different Browser
- If watching on a browser, try switching to Chrome or Firefox to see if the issue persists.

If trailers still don’t show after these, it might be related to Tubi’s service or a setting on your account. Let me know what happened with these steps, and if possible, please share any error messages you see. That will help me further assist you!