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Hi ShaunBosson,
It is not possible to prevent the specific group of users from Sync but as workaround as you mentioned we can disable sync option for whole SharePoint Site or specific Library.
For entire SharePoint Site:
Click on Gear Icon> Site Settings> Search and Offline availability (under Search)> Select No in Offline Client Availability> Ok
For Library:
Go to Library where you want to prevent from Sync> Click on Gear Icon> Library settings> Advanced settings> Select No in Offline Client Availability> Ok
Additionally, we suggest you provide a feedback in SharePoint UserVoice as related team can take into consideration by enabling disable sync option for a specific user group.
Thanks,
Chitrahaas