1013.1 Image before sign-in is NOT in focus

You mean this?

That's by design... guess Apple thinks it's cool or something.

You can replace it by doing the following:

Find the non-blurry version in: /System/Library/CoreServices/DefaultDesktop.jpg. If you use a custom wallpaper then just find that file instead.

Open it in Preview. Go to Tools > Adjust Size and make it 2880 x 1800. Then go to File > Export... and save it as PNG. Name it com.apple.desktop.admin.png.

Now open the folder: /Library/Caches, and paste the file there to replace the blurry version. The next time you start up, you should see the clear version now.

To prevent the system for overriding the changes, you can run the following Terminal command. Terminal is located in /Applications/Utilities.

chflags uchg /Library/Caches/com.apple.desktop.admin.png

To unlock the file again if you choose to do so later, open Terminal and type:

chflags nouchg /Library/Caches/com.apple.desktop.admin.png

That is by design and has been fo years, nothing new in 10.13.