Scroll down and click on Search and Indexing.
In the case of Avast at least, once you switch the shields back on, the Start menu search may continue working as it should. Click on Start > Settings > Update & Security > Troubleshoot. You could just try disabling your Avast shields temporarily, which should get the Start menu search back. Run the Windows Update Troubleshooter: Select Start > Settings > Update.
( Windows Defender itself has become a viable, secure option in recent years.) Try to install the update manually, by following the instructions above. You'll be notified if the problem was fixed or if there was a problem the troubleshooter couldn't fix.
Click on Start > Settings > Update & Security > Troubleshoot. From the Processes tab, scroll down until you find the Windows. Avast is one culprit, so try uninstalling that if you have it, then find an alternative if need be. Windows 10 built-in troubleshooters should at least identify, if not fix, your problem. If your Start menu stops working in Windows 10, heres what you can do to fix it. To be clear, we’re not suggesting here that you should disable and completely remove all third-party antivirus software from your device, but based on feedback here and across the Internet, certain programs cause Windows Search to malfunction. Disable/Restart Third-Party Antivirus, Enable Windows Firewall To do this, once again open the Settings app, and click ‘Search’.
In addition, running the SFC utility in Windows 10 Safe Mode could solve the problem for you, so that’s worth a shot if doing it in regular Windows 10 fails. To fix certain Windows 10 search problems, you need to rebuild Windows 10’s index database. Give that the Start menu search is a system process, any errors in it should be detected by using the SFC utility. This will scan your system files for any errors and corruptions and automatically attempt to fix them.