The XAMPP 7.0.5 installer for Windows is blurry in Windows 10 when the "Change the size of text, apps, and other apps" (i.e., display scaling) setting is set to a value greater than 100%. This setting can be accessed by right-clicking the desktop and selecting the "Display settings" menu item.
A workaround is to right-click the installer file, select the Properties menu item, and check the "Display display scaling on high DPI settings" option under the Compatibility tab of the Properties window that appears.