Hello,
Thank you for posting in Q&A forum.
Unfortunately, there is no direct Group Policy or Registry to place a background pattern behind the desktop icons. Windows itself does not support adding a background specifically behind the desktop icons, and Group Policy and Registry settings generally do not directly provide such customization. You may change the overall appearance and background of the desktop through the Personalization settings.
Thanks for your understanding.
I hope the information above is helpful.
Best Regards,
Yanhong Liu
============================================
If the Answer is helpful, please click "Accept Answer" and upvote it.