Hi CommunityNotification,
Welcome to the Microsoft community and thank you for asking your question in the community!
I understand that your problem is that you have set your desktop background as a slideshow on desktop 1, but after switching to the next desktop the desktop background automatically changes to a picture again.
But after my testing, it does not reproduce your problem. I think your problem may be due to a misconfiguration of the desktop background display due to a user profile error. I suggest you create a new local user to test if the problem still occurs.
You can create a new local account by following the steps below and switch to the newly created account to see if the feature is normal. Because this can't be ruled out due to incorrect configuration. Visit Create a local user or administrator account in Windows - Microsoft Support for more information.
Select Home > Settings > Accounts, and then select Family & Other Users. (On some versions of Windows, you'll see Other Users.)
Next to Add another user, select Add Account.
Select I don't have this person's sign-in information, and on the next page, select Add a user without a Microsoft account.
Enter a username, password, or password hint, or choose security questions, and then select Next.
Select Home > Settings > Accounts.
Under Family & Others, select the name of the account owner (you should see "Local Account" below the name), and then select Change Account Type.
Under Account Type, select Administrator, and then select OK.
Sign in with the new administrator account.
Note: If you choose an account that displays an email address or doesn't say "Local account," you're granting admin permissions to a Microsoft account, not a local account.
Note: If the new account is normal, do not delete the old account before backing up the data from the old account to avoid any data loss.
See if the problem still occurs after you switch to a new user.
Thank you again for your understanding and support! Please let me know if I have misunderstood. Tell us the results and we will get back to you as soon as possible. We look forward to hearing from you.
Best regards
Zhang Yang - MSFT | Microsoft Community Support Specialist