since the update to Edge Canary 85.0.535.0 the GPO setting for NewTabPageLocation is ignored for MDM controlled machines (couldn't test it for domain clients by now). Could you please take a look into it and bring the functionality back.
Btw, why is this feature enterprise only? You should give all users the opportunity to set their own custom New Tab Page (like Chrome does since ages). Please don't try to force people use Bing if they don't want. And don't you think it's quite inconsistent that we can change the default search provider but should use a New Tab Page that opens another one?