Endpoint analytics is a feature within Microsoft Intune specifically designed to provide insights into the performance and health of managed Windows devices. It includes a dedicated "Startup performance" report that analyzes boot and sign-in times, allowing administrators to review and troubleshoot slow startup processes. This report also includes a "Device restarts" tab, which provides a clear view of how often devices have been restarted over a given period. Therefore, Endpoint analytics is the most direct and purpose-built tool to meet the requirements of the question.

B. Device Management: This is a broad administrative category within the Intune portal, not a specific reporting or analytics tool for performance metrics.
C. Azure Monitor: While a powerful monitoring service, its primary focus is on Azure infrastructure and applications, not the built-in, detailed endpoint performance analysis provided by Endpoint analytics.
D. Intune Data Warehouse: This is a legacy feature for historical data reporting, which is being deprecated. It lacks the pre-built, user-friendly dashboards for startup performance that Endpoint analytics offers.

1. Microsoft Learn. "Startup performance in Endpoint analytics." Microsoft Intune documentation. This document explicitly states, "The startup performance score helps IT get users from power-on to productivity quickly, without lengthy boot and sign-in delays." It also details the "Device restarts" tab, which "displays a chart of the count of devices that have restarted in the last 7 days."

2. Microsoft Learn. "What is Endpoint analytics?" Microsoft Intune documentation. This overview confirms the feature's purpose: "Endpoint analytics can help identify policies or hardware issues that may be slowing down devices and help you proactively make improvements before end-users generate a help desk ticket... The following reports are available: Startup performance, Application reliability..."

3. Microsoft Learn. "Use the Intune Data Warehouse." Microsoft Intune documentation. This document notes the deprecation of the Data Warehouse: "The Intune Data Warehouse is being deprecated in favor of the Intune reporting API. The Intune reporting API provides a more modern and complete way to access your Intune data." This supports why it is not the recommended tool.