Hi, @john john ,
If you want to use an Organization asset library, it is required to enable CDN in your tenant during the setup. The asset library will be automatically set up as a CDN Origin, which means that library content will be replicated automatically to CDN service.
A Content Delivery Network, or CDN is a geographically distributed network consisting of proxy and file servers in datacenters connected by high-speed backbone networks. CDNs help keep Office 365 fast and reliable for end users. Cloud services like Office 365 use CDNs to cache static assets closer to the browsers requesting them to speed up downloads and reduce perceived end user latency. In short words, it simply provides better performance for end users. If you are interested in CDN, please read this.
If you really want to disable CDN, you can do it after the setup. It is not recommended for the performance sake. Use the cmdlet
More information about it:https://learn.microsoft.com/en-us/powershell/module/sharepoint-online/remove-spotenantcdnorigin?view=sharepoint-ps
An example here: https://techcommunity.microsoft.com/t5/sharepoint-developer/how-to-disable-public-cdn-for-particular-site-collection/m-p/138022
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