Hi @GCox ,
Unfortunately, there is no such Group Policy to control Clipboard permission. It can only be configured in Edge settings currently, and there seems to be no alternative to such a policy according to my investigation. I'm afraid that you have to add the sites manually. If you would like to have a related policy in the future, I suggest sending feedback to the Dev Team by pressing Alt+Shift+I.
UPDATE: Since Edge 109.0.1518.49, new policies have been introduced to control clipboard permission (per site). Please check the following 3 policies:
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Best Regards,
Shijie Li