User Configuration > Administrative Templates > Microsoft Office 2016 > Server Settings > SharePoint Server
User
HKCU\software\policies\microsoft\office\16.0\list\settings
The maximum number of rows fetched per request while populating a lookup in the SharePoint list control. Based on a standalone server's recommended hardware configuration a good default would be about 5000. The limit helps improve the performance of the SharePoint list control and is a defense in depth measure to prevent loading the server.