Hi,
In fact, this is not a network related question. Microsoft sign-in will always pop up when you use OneDrive, office 365 or open some Microsoft website which need Microsoft sign-in accounts.
Please first do a clean boot and check if Microsoft Sign-In still Pop Up, if not, then the Sign-In still Pop Up should related with your installed software.
For how to perform a clean boot in Windows 10, please refer to the following link:
How to perform a clean boot in Windows
Best Regards,
Candy
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