The outlook search option stopped working properly after WIndows10 update. According to numerous sources, The issue has happened after installing a security update from Windows (December 14, 2021—KB5008212).
Some reported that If They tried re-building the Indexing, it didn't resolve the problem. If you are savvy enough, you can uninstall that particular update and the search issue should be fixed. If you want to keep the update (KB5008212) which fixes other issues, you can try this work-around*:
1. In Windows, right-click Start, and then select Run. In the Open: box type regedit, and then click OK. This will open the registry editor.
2. Find this subkeen click it:
* HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows
3. Click Edit > New > Key and name the new key Windows Search.
4. Select the new Windows Search key.
5. Click Edit > New > DWORD Value.
6. Type PreventIndexingOutlook for the name of the DWORD, and then press Enter.
7. Right-click PreventIndexingOutlook, and then click Modify.
8. In the Value data box, type 1 to enable the registry entry, and then click OK.
9. Exit Registry Editor, and then restart Outlook.
Whenever you want to toggle back the Windows Desktop Search, you have to disable the PreventIndexingOutlook setting by typing 0 (zero) and clicking OK.
*NOTE: Editing the registry can cause irreparable harm to your system and steps must be taken to recover as we make no warranties nor guarantee for this workaround's effectiveness.