Generally, modems do not require additional drivers. You should first try the broadband connection that comes with Windows.

If you really need to install it, use window+r to call out the run window and enter regedit to return. Enter the Registry Editor.

Expand HKEY_CURRENT_USERSoftwarePoliciesMicrosoftWindows NTDriver Signing in turn

Create a new DWORD key named "BehaviorOnFailedVerify" with a key value of "0".

Driver signature is no longer required after restarting.