Greetings!
I'm Christine, an Independent Advisor and a Windows user like you. Looks like you would like to know why your Wallpaper keeps on changing. No worries, I got your back!
Based on your description, it looks like your background was set to Windows Spotlight that's why it keeps on changing. Windows Spotlight will show you new wallpaper or background each day. For more info about Spotlight, please check the link below:
Windows Spotlight:
https://learn.microsoft.com/en-us/windows/confi...
In case you would like to turn off the Windows Spotlight, you may follow the steps below:
Please click Start menu and type Background and hit enter.
Next to Personalize your lockscreen, you can choose Picture and set your preferred background from there.
https://support.microsoft.com/en-us/windows/cha...
Please let me know if you have any questions. I'll be happy to assist you all the way until it's resolved.
Thank you,
Christine L
Independent Advisor