Forcing Extensions on Safari

There is a DDM profile available for this. Jamf has announced that the option to manage extensions will come with the release of "Blueprints".

You can read about the declaration here and watch the keynote presentation about blueprints here.

Hopefully that helps! 

Is the DDM profile already available? 
TLDR: it's not out yet, as I'm understanding that?

i guess its not possible to Manage the Extension on Safari with MDM, you need to wait for the BluePrints to be released by JAMF in the upcoming versions. 

Also, be sure to file Feedback with Apple (use your Managed AppleID if you have one) requesting that Safari's extension management be improved to match the Chromium-based browsers.  Right now, Safari can be configured to allow extensions or block them, but compared to Chrome or Edge it cannot be set to force or allow some extensions but block everything else.

Further, the GUI is very confusing - even when set to block all extensions, Safari's preferences still show an Extensions button, and an end user may believe they have successfully installed an extension from the App Store even though it won't function. Many Safari extensions also install a 'stub' app into Applications, which can cause incorrect or false positive results in inventory.

This shortcoming of Safari is one reason my org won't be able to support it, compared to Edge - a so-called 'deployment blocker.'