Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
Force-disables spellcheck languages. Unrecognized languages in that list will be ignored. If you enable this policy, spellcheck will be disabled for the languages specified. The user can still enable or disable spellcheck for languages not in the list. If you do not set this policy, or disable it, there will be no change to the user's spellcheck preferences. If the 'SpellcheckEnabled' (Enable spellcheck) policy is set to disabled, this policy will have no effect. If a language is included in both the 'SpellcheckLanguage' (Enable specific spellcheck languages) and the 'SpellcheckLanguageBlocklist' policy, the spellcheck language is enabled. Example value: fr es