Zend certified PHP/Magento developer

How to update Windows 10 on an external boot drive

I have a Macbook Pro that I boot into Windows 10 via an external SSD running Windows 10 version 1803. I’d like to upgrade to Windows 10 1H2021, the current version, but windows update says I’m up to date, and the Windows Update Tool runs, downloads the update, and then halts telling me that “You can’t update windows if it’s on an external USB drive”.

So… how do I update my Windows 10 installation? Or do I need to wipe the drive and reinstall everything from scratch?

Thank you