You can use the following workaround to make yEd look better on your Windows 10 high-DPI display:
Right-click on the yEd application icon, such as via a shortcut on the desktop, and select "Properties". Then, select the "Compatibility" tab. Under settings, check the "Override high DPI scaling behavior" box. There are three options for this setting, "Application", "System", and "System (Enhanced)".
Use the second option, "System", to let the Windows 10 system control things, and then restart yEd to have the larger UI back.