Starting with Windows 10’s May 2019 Update, the login screen uses the blurred “Fluent Design” transparency found on the taskbar, Start menu, and elsewhere. If you’d like to see your lock screen background clearly, here’s how to disable the blur.
If you disable the lock screen, Windows 10 jumps right to the login screen instead, bypassing it. With the recent update, the background image has become distorted beyond recognition due to the “Acrylic”-style transparency effect used throughout Windows. Depending on what version of Windows 10 you have, these methods will bring clarity back to your background.
The Easy Way: Disable Transparency System-Wide
If you don’t like the look of the transparency effect, you can easily turn it off for all aspects of Windows 10. This will disable it not just on the lock screen, but also on the taskbar and right down to the Calculator or People apps. This method is an all-or-nothing approach and should only be disabled if you don’t enjoy the look anywhere on your desktop.
Open the Settings app and head to Settings > Personalization, or right-click an empty space on the Desktop, then click on “Personalise.”
Select “Colors” at the left side of the Settings window, scroll down until you see the option labeled “Transparency Effects,” then set it to “Off.”
To undo this change and enable the transparency effect on Windows 10, you can return here and toggle this feature to “On.”
Home Users: Disable Background Blur via the Registry
If you have Windows 10 Home, you’ll have to edit the Windows Registry to make these changes. You can also do it this way if you have Windows 10 Professional or Enterprise, but feel more comfortable working in the Registry as opposed to Group Policy Editor. (If you have Pro or Enterprise, though, we recommend using the easier Group Policy Editor, as described in the next section.
Read more: https://www.howtogeek.com/426554/how-to-disable-the-login-screens-background-blur-on-windows-10/