Hi Van, I am John J.D., a fellow Microsoft user like you.
I understand that you'd like to get the Day of the Dead icon back on your Search Highlights. Search Highlights can change based on the account's region and language settings. To make sure you see the event you want, please ensure that your account has the same region and language settings as your local account. You can adjust these settings by going to Settings > Time & Language > Region and Language.
If the issue persists, sometimes Search Highlights may not show the same icon for every user or every device due to Bing's dynamic content. In such cases, you might need to wait until the next day for the Search Highlights to update. I hope this helps, and if you have any more questions, feel free to ask!
John J.D.