Follow this to set wallpaper or screensaver in macOS Sonoma and above.

First of all Thank You.

I need to set custom wallpaper for all managed machines.

You set the image with a Restrictions Configuration Profile. If you want to define an image that does not already exist on the device, you just need to package the image and deploy it with a policy. 

Take a look at Desktoppr

Please refer this  https://learn.jamf.com/en-US/bundle/jamf-pro-documentation-current/page/Best_Practices_for_Computer_Configuration_Profiles.html#ariaid-title4

This is what we do as well