When did the issue start? Does the search return no results at all, or only some items?
Please try restarting the Windows Search process:
Press Ctrl + Alt + Delete and select Task Manager
Go to the Details tab
In the Name column, right-click SearchUI.exe or SearchHost.exe
Select End task, then confirm by clicking End process
After that, try using the search again and check if the issue persists.
Let me know how it goes.