When your monitor has a gratuitously high resolution Windows attempts to help you cope by choosing a high-DPI setting. The idea was to let you use the monitor's native resolution (very important for LCDs) while still having large enough text for you to read it. In other words it trades away screen real estate for readability by "magnifying" everything.

Most applications run in legacy mode, so everything gets scaled up through appcompat shims. This can distort text and bitmap graphics, producing blurring and pixilation.

Some programs can be more usable if you choose GDI Scaling for them ("System Enhanced" display appcompat), a feature in newer versions of Windows 10.

Programming to actually handle High DPI yourself is a big topic though.

This isn't a Windows 10 issue, it's an issue of buying too much monitor. Sadly we often don't have many options to avoid that. Otherwise display devices would be very cheap and profits too low.