Run the Search and Indexing Troubleshooter
The first thing you can do is run the Search and Indexing troubleshooter to see if it can help fix what might be preventing your search results from working.
Open Start > Settings > Update & security > Troubleshoot.
Scroll down, select Search and Indexing, click Run the troubleshooter, complete the wizard then restart. Then check to see if your search queries work.
are you using the dark theme?
try that and others here: https://www.groovypost.com/howto/fix-windows-10-search-index/