Hi Nick.
Thank you for answering.
Other people had the same question as me.
One of the answers mentioned a method of re-importing the site, so I tried that.
After that, the site started working successfully! amazing!
https://community.localwp.com/t/uh-oh-unable-to-start-update-7-2-1-on-windows-10/39259
By the way, what should I do to prevent errors like this from happening in the future?