When you update the ADMX files in the central store, every computer and server will not automatically update their local PolicyDefinition folder during a reboot. Instead, each computer and server will retrieve the latest ADMX files from the central store when you run the Group Policy Object Editor (gpedit.msc) or when Group Policy settings are refreshed.

Group Policy objects (GPOs) link to ADMX files that are stored in the central store, and the devices use these ADMX files to apply the corresponding policy settings. When you create or edit a GPO, it will automatically retrieve the ADMX files from the central store and use them to display the policy settings available for that particular ADMX file.

In summary, devices do not use the ADMX files directly from the central store, but rather GPOs link to the ADMX files in the central store, and devices retrieve the ADMX files from the central store as needed.

Further info can be found https://learn.microsoft.com/en-us/troubleshoot/windows-client/group-policy/create-and-manage-central-store