The pics W10 upgrade adds to show at startup...

...where are their file location? Since they aren't in Pictures.

 

C:\Windows\Web\Wallpaper

 

Actually none of those pics were ones I've seen.

Some were in "...web/screen".

One I was looking for, green fields atop a cliff at the sea, wasn't in any I've seen so far.

 

Is this what you are looking for perhaps?

https://www.alphr.com/find-windows-spotlight-lock-screen-images-windows-10/

On a side note, here are my wallpapers collection, which includes all laptop brands and the Windows 11 Wallpapers:

NBR Wallpapers Collection

Make sure to right-click on the file you just downloaded, go to Properties, then hit Unblock from the bottom right as it may be blocked since it was downloaded from the internet, if you don't do this before you extract it, the all the files will have a blocked status

To prevent this automatic blocking of files in the future so you don't have to go unblocking every file you download to ensure it runs properly, check the guide in this thread:
http://forum.notebookreview.com/threads/are-you-sure-you-want-to-run-this-file-yes-or-no.825668/

 

Thanks, I'll dig through that later.