Hi! If PC Health Check says the device is eligible but Windows Update doesn’t offer Windows 11 yet, first refresh the compatibility status. In Task Scheduler go to Task Scheduler Library > Microsoft > Windows > Application Experience, right-click Microsoft Compatibility Appraiser and choose Run, then return to Settings > Windows Update and Check for updates. Also confirm TPM 2.0 and Secure Boot are still enabled in firmware, and turn on Get the latest updates as soon as they’re available in Windows Update.
Finally, if that doesn't work, you can install using Microsoft’s official tools: the Windows 11 Installation Assistant for an in-place upgrade, back up your files, install any pending Windows 10 updates, temporarily disable third-party antivirus, and start the Assistant, it will re-check requirements and guide you through the upgrade.