Solution for changing Big Sur login wallpaper to custom.

This only works if/because you have one user, in which case the Mac will show the lockscreen picture of that user. As soon as you have multiple users, the Mac will show the default login screen. This is also why you have to deactivate the quest user in your solution... So, this is not really a solution

If the folder is not there create it!

make sure you write it correctly and capitalise it should be Desktop Pictures.Also make sure the folder named as your UUID is correct with no additional spaces at either beginning or end

I also have the same issue, and after following the instructions, have the same result. I want to clarify the distinction between the Big Sur default background we are trying to modify that comes up after boot or logout of user accounts, and the backgrounds that show up when choosing among the user profiles to log into from that initial screen. The instructions only address (and correct) the login backgrounds for individual user accounts, not the default Big Sur background that shows all available user login accounts. I even tried to activate root to access the default background, to no avail. This appears to be a minor bug that will take an engineering update to restore, much like the missing Books user-defined "View As" issue I previously sent in to Apple.

This solution is one I have seen elsewhere.

I have followed every step and checked, double checked but it doesn't seem to work.

So when I turn on my iMac I get the garish bright default horrid swirl of colours and the icons to click on for my wife's or my parts of the Mac. When click on either icon our own desktop photo shows when putting in our password.

I did see on other sites that its due to multiple users

I do now have to appologise. my bad, my mistake. I was creating the Desktop Pictures folder in /UID/lib../cashes/.... So I was doing my thing in the wrong directory.

After discovering that, and modifying the steps in the correct directory the magic happened.

thank all for the push in the right direction.

Love and Light from Belgium

LeadMare,

That's cool that you worked in the 90s and traveled with Apple's HIG team.

To get to your question, in Users and Groups click Login Options at the bottom of the list of users and you'll see underneath Automatic Login, display Login Window as: List of users or Name and Password. select List of users.

I believe for this to work, one needs to turn off FileVault and Guest user but understand you need it FileVault enabled for your job. Also it's Macintosh HD /Library/Caches/Desktop Pictures not your user folder directory.

Hope this helps.

This does not work on 2018 MBP I already had the uuid folder in my specified folder and Had the lock screen png I wanted, & that worked only after I selected a LOGIN USER, however the Startup screen prior to selecting a Login user is still that Awful Multicolored POS, This is the Screen we all want changed, I believe what we need to change are the BigSur.heic But what we cant find is the folder where the start screen is stored and Apple will not disclose that location...That said I assume if we can find the start screen pic location we can change it and problem solved....even If I delete the lockscreen.png everywhere it exists that hideous screen still exists, so this clearly isn't our soliution

Yes the fact that the "select user for login" screen is different from the password/lock screen, at least when there are multiple user accounts on the Mac, is well covered in the discussion on this question, and the filename of the file that controls that select user/login screen has been determined, but it is in a portion of the file system that you can't change without disabling SIP and SSV security -- see https://discussions.apple.com/thread/252056512?answerId=255286668022#255286668022 for details.

This method works!!!

But not until after I completely shut down the computers. Restart alone was not successful.

Thank you!

This fix does not seem to work on computers with multiple user accounts. It does however work when locking the screen, but the main login image remains the same.

Incorrect, this solution does work. If you read through the comments you'll find this solution only works for SINGLE user systems.

On my multi-user setup, Soren Pearson, my system automatically created and maintains the user (UUID) directories, in the /Library/Caches/Desktop Pictures directory. Complete with the corresponding lockscreen.png files.

The LoginScreen is still the “vivid” Big Sur graphic, but as soon as someone clicks on a User, to log in, the image changes to their LockScreen image (tied to their chosen Desktop image).

This all seems to be exactly as intended.

In the special case of a Single-User setup (when the system recognizes it as such), the system appears to skip the LoginScreen, since there is only a Single User that could possibly want to log in. So it goes straight to the LockScreen of the sole user of the machine.

The only remaining issue, then, is finding how to set the LoginScreen for multi-user systems (and those Single-User systems that, for whatever reason, are not recognized as such).