I would go with a pure mesh router system over using an extender and router combo. That is what I plan to do when I replace my current router. I also have an extender to cover a dead spot in my...

I do not understand why either. You may want to try the EN forum as this is the US one. They may have encountered the issue since they see the EU version a whole lot more....

Check the label on the router and see if it has a country code as your router may not have been a EU model. This may help https://www.tp-link.com/us/choose-your-location/

Sounds great. Have you done any recovery using the BackupBundle?

It is your Windows 10 that does not have SMB2. Google SMB2 for more info.

In your router USB settings, be sure the "network neighborhood" is enabled and the 'share mode' is on. Power cycle the router and the PC and try again.