“Unable to check upgrade status”

For hobbyists, pulling an old Lumia out of a drawer, sideloading the Upgrade Advisor, and watching it download Windows 10 Mobile one last time is a satisfying tech ritual. Just remember: it’s now a tinkerer’s OS, not a daily driver.

Q: Will I lose my data during the upgrade process? A: It's recommended that you backup your data before upgrading to Windows 10 Mobile to prevent any loss during the upgrade process.

The official app is no longer available for download from the Microsoft Store, as the store for Windows Phone 8.1 was permanently closed on December 16, 2019. Furthermore, Microsoft officially ended all support for Windows 10 Mobile in 2019. Current Status of the Upgrade Advisor

After the upgrade, the Upgrade Advisor can be uninstalled – it’s not needed for future updates.

for a more reliable, "semi-offline" upgrade process that doesn't rely on Microsoft's defunct mobile servers. 3. Important Considerations How to update a Windows 8 phone to Windows 10 Mobile

After the scan was complete, the app presented me with a detailed report. Fortunately, my device was compatible with Windows 10 Mobile, and the app provided a list of features that I could expect to enjoy with the upgrade.