If you have users complaining about incomplete search results on RDS Server 2019, especially in Outlook, this registry key might fix the problem. It did fix mine.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Search

DWORD EnablePerUserCatalog 0

Restart the Windows Search service.

This will create the index database under C:\ProgramData\Microsoft\Search\Data\Applications\Windows rather than in the user's AppData folder. It should look something like this: