Computer Configuration > Administrative Templates > Google Chrome
Both
HKLM\Software\Policies\Google\Chrome
Setting the policy to Enabled turns spellcheck on, and users can't turn it off. On Microsoft® Windows®, Google ChromeOS and Linux®, spellcheck languages can be switched on or off individually, so users can still turn spellcheck off by switching off every spellcheck language. To avoid that, use the SpellcheckLanguage to force-enable specific spellcheck languages. Setting the policy to Disabled turns off spellcheck from all sources, and users can't turn it on. The SpellCheckServiceEnabled, SpellcheckLanguage and SpellcheckLanguageBlocklist policies have no effect when this policy is set to False. Leaving the policy unset lets users turn spellcheck on or off in the language settings.