Using the AirPort Time Capsule as a backup site for the Win 10 laptop - New Problem

The issue is likely that Microsoft removed SMBV1......a communication protocol used to connect the Mac to the network hard drive.......from Windows 10.

Things worked previously likely because the laptop was already connected to the Time Capsule when you installed the new operating system,, but Windows 10 now views your attempt to connect to the Time Capsule as a new connection which they will not allow due to serious security concerns with the old SMBV1 protocol used by older devices......like a Time Capsule.

A temporarily solution might be to enable SMBV1 on Windows 10 to access data if Windows 10 still allows you to do this. There have been some discussions about whether Microsoft would continue to allow users to do this, but I do not know if they still allow the workaround.......which Microsoft considers to be a serious security threat.

More info here:

https://www.windowscentral.com/how-access-files-network-devices-using-smbv1-windows-10

For what its worth, Microsoft does not call this a "workaround". They would call it a serious security threat, which is the reason why they disababled SMBV1.

It's your call though.