Hi @Victor Miller ,
I'm afraid there is no GPO or registry setting can block OneDrive sync capabilities. As said in Block syncing OneDrive accounts for specific organizations and Allow syncing OneDrive accounts for only specific organizations, you have to specify tenant IDs to enable these settings which means that these settings that make use of it should be considered non-applicable as there is no Tenant ID with SharepOint on-premise.
The only alternative method I could think of is that you can disable Offline Client Availability on each site via go to site settings -> Search and Offline Availability.
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