Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
The Microsoft Editor service provides enhanced spell and grammar checking for editable text fields on web pages. If you enable or don't configure this policy, Microsoft Editor spell check can be used for eligible text fields. If you disable this policy, spell check can only be provided by local engines that use platform or Hunspell services. The results from these engines might be less informative than the results Microsoft Editor can provide. If the 'SpellcheckEnabled' (Enable spellcheck) policy is set to disabled, or the user disables spell checking in the settings page, this policy will have no effect.